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UBf'ARy 

OF  THE 

UNIVERSITY  OF  ILLINOIS 


WON  CIRCULATING 


UNIVERSITY  OF  ILLINOIS 
Agricultural    Experiment    Station 


BULLETIN  No.  178 


RECENT  ILLINOIS    WORK   ON  THE  CORN 

ROOT-APHIS   AND   THE  CONTROL 

OF  ITS   INJURIES 


BY   STEPHEN   A.   FORBES 
STATE  ENTOMOLOGIST 


URBANA,   ILLINOIS,   JANUARY,  1915 


RECENT   ILLINOIS    WORK  ON  THE  CORN 

ROOT-APHIS    AND   THE   CONTROL 

OF   ITS   INJURIES 

BY  STEPHEN  A.  FORBES,  STATE  ENTOMOLOGIST 

The  corn  root-aphis,  or  corn  root-louse,  as  it  is  more  commonly 
called,  is  now  the  most  generally  injurious  insect  pest  of  the  corn  field 
in  Illinois.  Its  injuries  have  been  but  little  checked  by  all  that  has  been 
done  and  printed  concerning  it,  and  they  are  evidently  increasing  slow- 
ly in  total  effect.  There  is,  in  fact,  no  other  corn-field  insect  which  is 
so  frequently  called  to  the  attention  of  the  economic  entomologist. 
Nevertheless,  the  corn-root-aphis  problem  has  been  practically  solved 
— not,  perhaps,  in  the  best  way  possible,  or  as  completely  as  will  be  the 
case  when  time,  money,  and  skilled  assistance  are  all  available  for  fur- 
ther studies  and  experiments.  Undoubtedly,  however,  if  the  results 
which  have  already  been  established  were  generally  put  to  use  in  the 
practice  of  the  Illinois  farmer,  this  aphis  would  presently  lose  its  place 
at  the  head  of  the  list  of  insects  affecting  corn,  and  would  be  classed 
among  those  which  are  only  occasionally  injurious  enough  to  call  for 
special  notice. 

It  is  the  purpose  of  this  article  to  set  forth  the  results  of  our  more 
recent  investigations  and  experiments  (1907-1910)  in  all  necessary  de- 
tail, and  to  show  what  they  signify  and  how  they  apply  to  the  routine 
of  corn  culture  in  this  state. 

The  key  to  the  control  of  this  insect  is  to  be  found  in  its  spring 
condition  in  old  corn  fields  which  have  been  infested  by  it  the  year 
preceding ;  and  in  the  fact  that  corn  is  the  only  crop-plant  upon  which 
it  lives  and  multiplies.  This  is  substantially  shown  by  the  following 
facts. 

1.  The  eggs  left  by  the  corn  root-lice  in  fall  when  the  insects 
themselves  perish,  are  virtually  all  in  the  earth  in  corn  fields.     They 
are  collected  there  by  the  corn-field  ant,  which  keeps  them  in  its  un- 
derground burrows  until  they  hatch  the  following  April  and  May. 

2.  As  the  young  root-lice  escape  from  the  egg  they  are  placed  by 
these  ants  on  the  roots  of  pigeon-grass,  smartweed,  and  other  corn- 
field weeds,  on  which  they  live  by  sucking  the  sap,  giving  off  at  the 
same  time  an  abundant  fluid  excrement  which  is  lapped  up  by  the 
ants  as  food. 

3.  The  root-lice  hatching  from  the  egg  are  all  females,  and  pro- 
duce no  eggs,  but  bring  forth  living  young  when  they  themselves  are 


406  BULLETIN  No.  178  [January, 

about  two  weeks  old.  Their  young,  in  turn,  reproduce  in  the  same 
way,  one  generation  succeeding  another  at  shorter  intervals  as  the 
weather  warms  up,  until  in  midsummer  they  are  only  a  week  apart. 
The  average  number  of  complete  generations  for  the  season  is  about 
sixteen  in  the  latitude  of  central  Illinois. 

4.  The  second  generation  of  this  series  begins  to  appear  in  cen- 
tral Illinois  about  the  first  of  May,  and  the  oldest  of  these  will  begin 
to  give  birth  to  the  third  generation  on  or  before  the  middle  of  that 
month.    So  rapid  is  the  rate  of  reproduction  that  by  the  end  of  June 
as  many  as  six  generations  may  have  made  their  appearance. 

5.  The  root-lice  of  the  first  generation — those  hatching  from  the 
egg — are  all  wingless ;  but  beginning  with  the  second  generation  a  vari- 
able percentage  of  this  and  of  all  following  generations  may  acquire 
wings.     These  winged  root-lice,  called  migrants,  may  thus  begin  to 
appear  early  in  May. 

6.  By  means  of  these  winged    insects    originating    in    old    corn 
ground,  fields  not  infested  the  year  before  may  become  infested  from 
the  first  week  in  May  onward.     Root-aphis  injury  is  thus  like  a  con- 
tagious disease,  spreading  from  field  to  field  on  the  wings  of  the  es- 
caping migrants.    As  these  fall  to  the  ground  they  are  taken  in  charge 
by  the  corn-field  ant,  which  carries  them  under   ground    and    places 
them  on  the  roots  of  plants,  where  they  begin  to  feed  and  to  bring 
forth  living  young  precisely  as  do  the  wingless  ones.    The  young  born 
from   winged   mothers   are  wingless  or  winged,  according  to  circum- 
stances, just  as  are  those  whose  mothers  are  themselves  without  wings. 

7.  As  the  winged  lice  may  begin  to  come  up  out  of  the  ground 
and  fly  away  even  before  corn  is  planted  for  the  new  crop,  and  will 
continue  to  do  so  thruout  the  season,  fields  that  were  not  in  corn 
the  year  before  may  become  infested  by  these  winged  migrants  and 
their  young  while  the  corn  is  still  very  small. 

8.  The  corn-field  ant  is  indispensable  to  the  root-lice,  which  it 
carries  about  from  place  to  place  as  may  be  necessary,  transferring 
them  to  the  roots  of  fresh  plants  when  those  they  have  been  feeding 
upon  become  sapped  or  overcrowded. 

9.  If  an  old  infested  corn  field  is  planted  to  some  other  crop  than 
corn,  the  root-lice  living  in  it  feed  on  the  weeds  until  these  are  smoth- 
ered out  by  the  new  crop-plants.     Many  of  them  then  acquire  wings 
and  fly  away,  and  others  are  eaten  by  the  ants  which  have  them  in 
charge.    The  field  is  in  this  way  virtually  cleared  of  them ;  but  the  sur- 
vivors are  widely  dispersed,  to  infest  other  fields. 

10.  If  an  old  infested  corn  field  is  planted  to  corn,  the  lice,  placed 
at  first  on  the  roots  of  the  corn-field  weeds,  are  transferred  by  the 


<'9/5J  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS   INJURIES  407 

ants  to  the  roots  of  the  corn  plants  as  the  weeds  in  the  field  are  de- 
stroyed by  cultivation,,  and  there  they  continue  to  multiply  the  whole 
season  thru. 

11.  The  corn  root-louse  may  live  and  propagate  thru  the  sea- 
son on  a  considerable  variety  of  other  plants,  including  several  com- 
mon weeds,  but  on  none  of  them  in  numbers  to  make  the  fact  a  matter 
of  serious  economic  importance.    Injury  to  corn  by  root-lice  is  almost 
wholly  due  to  those  which  have  fed  and  bred  in  fields  of  corn,  and  not 
to  the.  comparatively  scanty  stock  which  lives  on  other  plants.     From 
this  it  appears  that  if  they  are  generally  prevented  from  getting  a  start 
in  corn  fields  in  spring,  their  injury  to  corn  will  be  insignificant. 

12.  The  root-lice  may  be  most  easily  destroyed  in  early  spring, 
and  a  strong  check  may  also  be  put  upon  the  multiplication  of  the 
corn-field  ants  by  early  plowing  of  old  corn  fields  to  a  depth  of  six  or 
seven  inches,  followed  by  repeated  deep  disking  as  a  preparation  of  the 
ground  for  corn.     This  treatment  acts  by  killing  and  keeping  down 
the  young  weeds  on  which  the  root-lice  are  feeding,  and  by  breaking 
up  the  burrows  of  the  ants  and  scattering  the  eggs  and  young  of  the 
root-lice  and  the  eggs  and  young  of  the  ants  themselves  thru  the  dirt 
so  thoroly  that  the  ants  can  not  recover  their. property  even  if  they 
remake  their  nests. 

13.  As  corn  planted  on  ground  not  in  that  crop  the  year  before 
may  become  infested  by  winged  root-lice  from  neglected  fields  of  last 
year's  corn,  anything  like  a  general  control  of  the  injury  requires  a 
general  clearing  up  of  old  infested  fields  in  spring.    So  far  as  possible, 
any  such  fields  should  be  treated  as  prescribed  under  No.  12,  both  as 
a  protection,  of  one's  own  corn  crop,  which  is  likely  to  be  first  and 
most  heavily  infested,  as  a  rule,  by  the  root-lice  of  one's  own  raising, 
and  also  as  a  duty  to  one's  neighbors,  whose  crops  should  not  be  left 
to  suffer  injury  because  of  one's  own  negligence. 

14.  When  this  program  of  preventive  preparation  of  old  corn 
fields  can  not  be  fully  carried  out,  some  temporary  advantage  may 
sometimes  be  gained  in  the  beginning  by  planting  with  the  seed  sub- 
stances so  offensive  and  repellent  to  the  ants  that  they  will  keep  out 
of  the  hill  until  these  have  disappeared.     Such  substances  are  oil  of 
tansy,  tincture  of  asafetida,  oil  of  sassafras,  anise  oil,  kerosene,  oil  of 
lemon,  and  a  number  of  other  volatile  oils  and  strong-smelling  sub- 
stances, the  vapors  from  which  the  corn-field  ants  can  not  endure. 
These  fluids  were  formerly  used  by  mixing  the  seed  with  them  direct, 


8  BULLETIN  No.  178  [January, 

ut  applied  in  this  way  they  are  likely,  under  certain  weather  condi- 
.ions,  to  be  injurious  to  the  kernel  and  to  the  young  plant.1 

15.  While  there  is  no  evidence  that  the  corn  root-aphis  thrives 
best  on  comparatively  unthrifty  plants,  as  do  many  other  insects,  it  is 
sure  that  the  corn  plant  endures  the  drain  of  its  infestation  with  less 
injury  when  the  soil  is  fertile  and  the  corn  well  cared  for.    The  good 
corn-farmer  on  a  good  corn-farm  will  consequently  suffer  less  from 
this  insect,  as  a  rule,  than  his  less  careful  and  less  fortunate  neighbor. 

16.  A  frequent  rotation  of  crops,  with  a  short  period  in  corn,  is 
a  most  valuable  measure  of  prevention  against  root-louse  injury,  since 
corn  following  some  other  crop  than  corn  can  only  become  infested 
by  means  of  root-lice  coming  into  it  from  outside  fields. 

17.  The  more  generally  correct  practices  are    followed    in    any 
neighborhood  the  less  will  be  the  injury  done  by  the  root-aphis  to 
the  fields  even  of  those  who  pay  no  attention  to  it.    On  the  other  hand, 
a  general  neglect  of  it  will  give  it  such  opportunities  of  multiplication 
that  it  will  swarm  out  of  infested  fields  in  numbers  to  give  its  attacks 
the  character  of  an  epidemic.     It  is  consequently  to  the  interest  of 
every  one  to  do  his  best  to  establish  the  correct  routine  of  corn  culture 
thruout  his  neighborhood,  as  well  as  to  follow  it  carefully  himself. 

18.  Finally,  to  prevent  mistakes,  the  fact  should  be  known  that  a 
few  other  kinds  of  root-lice  are  likely  to  infest  the  roots  of  corn  tem- 
porarily, even  when  the  crop  is  planted  on  ground  not  in  corn  the  year 
before.  Certain  grass  root-lice  and  clover  root-lice  may  live  for  a  time 
on  corn,  and  may  even  do  some  injury  in  early  spring,  leaving  the 
fields,  however,  before  the  summer  is  over. 

RECENT  ARTICLES  IN  THE  OFFICE  REPORTS 

My  latest  articles  on  the  corn  root-aphis,  giving  the  results  of  ex- 
periments in  detail,  were  published  in  1908  and  1909  in  my  Thirteenth 
and  Fourteenth  reports.  The  first  of  these  articles  gives  an  account 
of  several  field  experiments  made  in  1904  and  1905,  with  deep  plowing 
and  repeated  disking  of  infested  fields  as  a  preparation  of  the  ground 
for  planting;  and  the  second  article  describes  a  long  series  of  experi- 
ments made  in  1905  and  1906,  in  the  insectary  and  in  the  field,  with 
various  repellent  substances  applied  to  the  seed  at  planting  with  a 
view  to  excluding  the  ants  and  the  root-lice  from  the  hills. 


statement  concerning  conditions  under  which  seed-corn  may  be  injured 
by  kerosene  and  other  oils  is  based  upon  extensive  and  very  careful  experi- 
ments made  by  Dr.  J.  H.  Whitten  when  he  was  a  graduate  student  in  botany 
at  the  University  of  Illinois.  The  results  of  these  experiments  have  now  been 
published  by  him  in  detail  in  the  Bulletin  of  the  Illinois  State  Laboratory  of 
Natural  History,  Volume  X,  Article  V. 


/o/5]  CORN  ROOT- APHIS  AND  CONTROL  OF  ITS  INJURIES  409 

In  the  first  article1  it  was  shown  that  after  the  usual  plowing  and 
harrowing  as  a  preparation  for  corn,  disking  three  times  additional 
and  harrowing  once  had  the  effect  to  reduce  the  number  of  root-lice 
on  the  experimental  plots  92  per  cent,  and  the  number  of  hills  in- 
fested by  root-lice  82  per  cent;  and  to  reduce  the  number  of  ants  92 
per  cent  and  the  number  of  hills  infested  by  ants  64  per  cent.  It  was 
further  shown  that  twice  disking  reduced  the  number  of  root-lice  84 
per  cent  and  the  number  of  hills  infested  by  them  75  per  cent,  the  num- 
ber of  ants  65  per  cent  and  the  number  of  hills  infested  by  them  59 
per  cent ;  and  that  once  disking  reduced  the  root-lice  and  hills  infested 
by  them  43  per  cent  and  41  per  cent,  and  the  ants  and  hills  infested  by 
them  42  per  cent  and  33  per  cent,  respectively.  All  these  ratios  were 
determined  in  each  case  by  comparison  with  check  plots  in  the  same 
fields  which  had  received  only  the  usual  preparation  for  corn. 

These  facts,  taken  by  themselves,  seem  thoroly  conclusive  and 
highly  satisfactory.  Nevertheless,  since  corn  root-lice,  like  most  in- 
jurious insects,  are  largely  affected  by  the  varying  conditions  of 
weather,  soil,  and  crop,  it  was  thought  necessary  to  test  these  conclu- 
sions by  repeating  and  varying  the  above  experiments  in  a  way  to  ar- 
rive at  maximum,  minimum,  and  average  benefits  under  the  varying 
phases  and  practices  of  Illinois  agriculture.  It  is  a  part  of  the  purpose 
of  this  article  to  give  the  product  of  these  later  experimental  studies 
in  detail. 

The  second  article  above  referred  to,2  that  published  in  my  Four- 
teenth Report,  dealt  especially  with  the  effects  of  the  treatment  of  seed- 
corn  with  oil  of  lemon,  carbolic  acid,  formalin,  and  pure  kerosene, 
with  the  general  result  that  under  the  conditions  of  1906,  where  seed- 
corn  was  treated  with  oil  of  lemon  just  before  planting  in  infested 
fields,  the  yield  was  increased  by  1,159  ear-bearing  stalks  to  the  acre, 
while  a  similar  treatment  of  the  seed  with  carbolic  acid  increased  the 
yield  by  945  such  stalks,  a  formalin  treatment  by  742,  and  a  kerosene 
treatment  by  274.3 

Notwithstanding  this  surprisingly  favorable  result,  there  was  some 
appearance  of  injury  to  the  seed  by  all  these  substances.  The  check- 
plot  contained  more  living  hills  to  the  80-rod  row  than  any  of  the  ex- 
perimental plots,  the  difference  being  small,  however,  except  in  the 


1  Field  Experiments  on  the  Corn  Root-aphis    (Aphis  maidiradicis  Forbes). 
24th  Rep.  State  Ent.  111.,  pp.  8-29.    See  especially  the  table  on  p.  29. 

'Experiments  with  Repellents  against  the  Corn  Root-aphis,   1905  and  1906. 
25th  Rep.  State  Ent.  111.,  pp.  1-26. 

325th  Rep.  State  Ent.  111.,  p.  21. 


410  BULLETIN  No.  178  [January, 

plot  treated  with  kerosene,  the  hills  in  which  numbered  only  82.5  per 
cent  of  those  in  the  check. 

The  whole  operation  of  this  year  was  regarded  as  provisional 
only,  and,  in  the  language  of  my  report,  its  conclusions  were  "taken  as 
applying  exactly  only  to  similar,  if  not  identical,  conditions — a  similar 
soil  similarly  prepared,  equally  infested  with  the  corn  root-aphis,  and 
subject  to  similar  weather  conditions — and  with  a  treatment  of  seed 
identical  with  ours  in  all  particulars,  including  materials  of  the  same 
quality  and  strength.  How  far  the  results  here  described  may  be  ex- 
pected to  apply  to  a  different  soil,  less  heavily,  or  even  much  more 
heavily,  infested,  more  thoroly  prepared,  and  planted  during  either 
a  very  wet  spring  or  a  very  dry  one,  with  a  less  perfect  seed,  treated 
with  slightly  different  chemicals  and  compounds,  can  be  learned  only 
by  repeated  and  varied  experiment."1  As  will  be  seen  from  later 
studies  described  in  this  paper,  this  cautionary  remark  has  been  jus- 
tified by  the  fact  that  no  equally  favorable  result  has  been  obtained 
since  1906. 

LIST  OF  OPERATIONS  HERE  REPORTED 
1907 

1.  Field  experiments  with  repellents,  near  Leroy,  McLean  county, 
in  charge  of  E.  O.  G.  Kelly  and  J.  J.  Davis. 

2.  Field  experiments  with  repellents  by  the  Bloomington  Canning 
Company,  near  Normal,  McLean  county,  reported  by  J.  A.  West. 

3.  Laboratory  experiments  made  by  J.  J.  Davis  with  the  effect 
on  seed-corn  produced  by  ordinary  lemon  oil,  by  lemon  oil  from  which 
the  terpenes  had  been  extracted,  and  by  the  terpenes  themselves. 

1908 

4.  Field  experiments  near  Galesburg,  Knox  county,  supervised  by 
J.  A.  West,  but  in  immediate  charge  of  G.  E.  Sanders.    In  these  ex- 
periments various  repellents  were  applied  to  the  seed,  and  the  soil  was 
variously  prepared  for  planting  by  plowing  to  different  depths,  by 
disking  different  numbers  of  times,  and  by  plowing  in  fall  and  spring. 
A  comparison  was  also  made  of  infestation  and  injuries  by  root-lice 
to  a  plot  of  corn  on  old  oats-ground  and  to  corn  on  old  corn-ground. 

1909 

5.  Field  experiments  near  Bloomington,  McLean  county,  in  joint 
charge  of  G.  E.  Sanders  and  W.  P.  Flint.    This  was  essentially  an  ex- 


Rep.  State  Ent.  111.,  p.  22. 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


419 


The  inference  that  terpeneless  oil  of  lemon,  produced  by  distilling 
off  the  more  volatile  terpenes  from  the  ordinary  oil,  is  more  likely  to 
be  injurious  to  seed-corn  than  either  the  terpenes  or  the  crude  oil,  is 
confirmed  in  an  interesting  manner  by  the  results  of  experiments  de- 
scribed by  Dr.  Whitten  in  the  paper  already  referred  to,  in  which  he 
says :  "At  the  present  the  trend  of  evidence  tends  to  show  that  the 
[corn]  grains  bear  immersion  in  the  lighter  oils  without  injury  for 
much  longer  periods  than  in  the  heavier  oils,  and  that  the  injurious 
after-effects  of  the  latter  are  more  pronounced  than  those  of  the 
former."1 

As  a  general  conclusion  from  this  phase  of  my  discussion,  it  may 
be  said  that  my  supposition  that  injury  to  planted  seed-corn  near 
Bloomington  was  owing  to  differences  in  the  quality  of  the  oils  applied 
to  the  seed,  was  unfounded;  and  the  cause  of  the  observed  variation  in 
the  effects  of  treatment  must  be  sought  elsewhere. 

As  a  further  test  of  this  conclusion  we  may  take  two  sets  of  plant- 
ings, made  at  the  insectary,  in  which  the  seed  was  treated  with  the 
same  lemon  oils,  in  mixtures  of  the  same  strengths,  as  were  used  by 
Mr.  W.  R.  Scott,  of  Knoxville,  and  Mr.  Frank  Clark,  of  De  Long,  two 
Knox  county  farmers  who  reported  serious  injury  to  their  seed.  Sam- 
ples of  the  oils  were  obtained  from  these  farmers  with  statements  of 
the  strengths  used  by  them.  Both  bought  their  lemon  oil  in  Knox- 
ville, but  from  different  druggists.  From  the  following  table  it  will  be 
seen  that  the  insectary  plantings  of  seed  treated  with  these  oils  yielded 
results  not  materially  different  from  those  of  the  untreated  check- 
plantings  made  at  the  same  time ;  and  the  injury  reported  must  hence 
have  been  due  to  some  local  cause. 

POT  PLANTINGS  TREATED  WITH  ORDINARY  LEMON  OIL  AND  ALCOHOL  AS  USED 
BY  W.  R.  SCOTT  AND  FRANK  CLARK.    EXPERIMENT  OF  SEPTEMBER  22,  1907 


MH     0) 

Per  cent  of  plants  up 

•£  t! 

Insectary  test 

6    *•« 

_b/.O 

°v  tn 

•* 

September 

October 

>  V 

29 

30 

3 

7 

<.£ 

Scott's    sample    

200 

3 

49 

79 

81 

6  2 

Clark's   sample    

600 

2 

21 

76 

79 

5  5 

Checks    

250 

0 

31 

81 

83     1    6.1 

Bulletin,   Illinois   State  Laboratory  of    Natural  History,   Vol.  X,   Art.  V, 
p.  269. 


420  BULLETIN  No.  178  [January, 

CONTRIBUTING    CAUSE  OF   INJURY   TO   SEED-CORN    BY    REPELLENTS 

That  the  cause  was  indeed  local  is  indicated  by  the  fact  that  in  a 
prolonged  trip,  through  central  Illinois,  made  during  the  summer  of 
1907,  for  an  inquiry  concerning  the  use  of  lemon  oil  and  its  results, 
Mr.  Davis  found  a  general  complaint  of  injury  to  the  seed  in  the 
vicinity  of  Galesburg,  arid  especially  between  Knoxville  and  De  Long. 
In  all  of  the  territory  covered  by  his  trip  the  lemon-oil  treatment  had 
been  more  or  less  used  in  practically  all  localities  except  in  Christian 
county,  and  there  was  commonly  no  report  of  injury  to  the  seed,  the 
main  complaint  of  the  farmers  being  the  fact  that  they  found  no  dif- 
ference in  respect  to  thrift  and  stand  between  treated  and  untreated 
corn. 

What  the  local  cause  of  injury  probably  was  in  these  various  cases 
is  shown  by  the  record  of  rainfall  at  Bloomington,  given  on  a  preced- 
ing page,  taken  in  connection  with  the  proof  contained  in  Dr.  Whit- 
ten's  studies,  already  referred  to,  that  kerosene  and  other  volatile  oils 
are  injurious  to  seed-corn  in  proportion  to  the  amount  of  moisture  in 
the  ground  during  the  planting  and  germinating  period.  In  discussing 
his  own  experiments,  Dr.  Whitten  says : 

"When  the  amount  of  water  in  the  soil  was  reduced  from  30% 
saturation  to  25  %  saturation,  the  per  cent,  of  germination  was  increased 
and  the  growth  of  the  seedlings  was  more  nearly  normal ;  but  when  the 
water  content  of  the  soil  was  increased  to  50  or  75%  saturation,  the 
per  cent,  of  germination  was  markedly  decreased  and  the  subsequent 
growth  of  many  of  the  seedlings  abnormal."  Again  he  says :  "It  is 
evident  that  within  certain  limits  the  seedlings  are  not  injured  by  the 
oil  present  at  the  time  of  planting,  provided  growth  is  initiated  in  the 
presence  of  a  minimum  amount  of  water.  The  small  quantities  of 
kerosene  are  toxic  in  proportion  to  the  increase  of  the  moisture  con- 
tent of  the  soil.  In  the  50  and  75 %  saturated  soils  the  dormant  period 
of  the  grain  is  always  less  than  36  hours,  while  in  the  25%  saturation 
the  time  is  extended  to  approximately  five  days.  This  increase  of  time 
affords  the  seedling  an  opportunity  to  dispose  of  the  oils  much  more 
slowly,  and  it  does  so  without  injurious  effects."1 

The  Bloomington  rainfall  of  nearly  two  and  three-quarters  inches 
distributed  over  seven  days  and  including  the  planting  period  of  the 
Normal  field,  must  have  kept  the  ground  unusually  moist  from  the  be- 
ginning, and  is  a  sufficient  explanation  of  the  injury  to  seed-corn  in 
that  field.  Unfortunately,  I  can  obtain  no  weather  record  of  a  place 


'Bull.  111.  State  Lab.  Nat.  Hist.,  Vol.  X,  Art.  V,  pp.  266-267,  268. 


/9/5l  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS   INJURIES  421 

where  no  injury  was  done,  for  comparison  with  the  Bloomington  ob- 
servations, and  to  that  extent  the  proof  must  remain  incomplete. 

FIELD   EXPERIMENTS    WITH    REPELLENTS,    1907 

I  have  next  to  report  the  purely  negative  results  of  a  series  of 
field  experiments  and  observations  begun  in  April,  1907,  at  Le  Roy, 
McLean  county,  by  one  of  my  field  assistants,  Mr.  E.  O.  G.  Kelly,  and 
continued  by  Mr.  John  J.  Davis,  to  whom  the  problem  was  transferred 
in  the  latter  part  of  June.  In  these  experiments,  intended  as  a  partial 
repetition  and  verification  of  those  made  at  Elliott,  in  Ford  county,  in 
1906,1  no  injury  was  done  to  the  seed  by  oil  of  lemon  and  alcohol,  oil 
of  citronella  and  alcohol,  carbolic  acid,  pure  kerosene,  or  pure  turpen- 
tine, each  applied  in  the  proportions  commonly  used  by  us  at  this 
time;  nor  was  any  difference  discernible  between  experimental  and 
check  plots  in  the  degree  of  infestation  by  the  ants  or  by  the  aphids. 
Both  the  observers^  atttributed  the  results  to  heavy  flooding  rains 
which  fell  at  intervals  during  the  whole  planting-period,  and  which 
washed  away  the  fluid  repellents  so  thoroly  that  the  seed  no  longer 
smelled  of  them.  At  the  same  time  root-lice  virtually  disappeared 
from  fields  which  had  been  especially  selected  for  experiment  because 
they  were  so  heavily  infested  by  ants  before  planting  that  it  seemed 
certain  that  the  corn  would  be  seriously  injured  by  root-lice  unless  it 
was  artificially  protected.  Rains  fell  here,  in^short,  at  a  time  and  in  an 
amount  both  to  drown  out  the  root-lice  and  to  wash  away  the  re- 
pellents before  the  seed  could  be  injured. 

The  following  is  an  outline  of  the  more  important  of  these  ex- 
periments. 

Experiment  1. — A  field  of  thirty  acres,  on  which  corn  was  grown 
in  1906,  preceded  by  oats  in  1905.  The  seed  used  in  planting  was 
dealt  with  as  follows :  that  for  16  rows,  was  treated  with  a  fourth 
of  an  ounce  of  kerosene  to  the  gallon  of  seed ;  for  24  rows,  with  a 
half  ounce  of  kerosene  to  the  gallon;  for  68  rows,  untreated  and  re- 
served as  a  check ;  for  44  rows,  treated  with  three-fourths  of  an  ounce 
of  kerosene;  for  62  rows,  with  three  ounces  per  gallon  of  a  mixture 
of  oil  of  lemon  (10  per  cent)  and  alcohol  (90  per  cent)  ;  and  for  10 
rows,  untreated,  as  an  additional  check. 

The  field  was  planted  on  the  llth  of  May,  1907,  and  on  the  20th 
of  May  no  odor  of  kerosene  or  oil  of  lemon  could  be  detected  on  the 
treated  seed.  On  the  28th  of  May,  many  hills  were  burrowed  by  ants, 
but  an  examination  of  fifty  such  hills,  dug  up  for  the  purpose,  dis- 


Rep.  State  Ent.  111.,  p.  14. 


422 


BULLETIN  No.  178 


[January, 


closed  no  root-lice.  On  the  31st  of  May  a  few  root-lice  were  found. 
On  the  6th  of  June  an  examination  of  two  hundred  hills  dug  up  gave 
the  following  averages: 

Check  plots,  50  hills  examined.  Six  hundred  and  thirty-eight 
adult  ants,  no  ant  larvae,  7  root-lice. 

Plot  treated  with  half  an  ounce  of  kerosene  to  the  gallon  of  seed, 
50  hills  examined.  Two  hundred  and  ninety-four  adult  ants,  400 
larvae,  no  root-lice. 

Plot  treated  with  three-fourths  of  an  ounce  of  kerosene  to  the 
gallon  of  seed,  50  hills  examined.  Six  hundred  and  forty-one  adult 
ants,  500  larvae,  14  root-lice. 

Plot  treated  with  a  10  per  cent  solution  of  oil  of  lemon  at  the  rate 
of  three  ounces  per  gallon  of  seed,  50  hills  examined.  Seven  hundred 
and  thirty-two  adult  ants,  400  larvae,  26  root-lice. 

Taking  the  four  plots  together,  2,305  adult  ants  and  1,300  ant 
larvae  were  found  in  two  hundred  hills,  but  these  were  accompanied  by 
only  47  root-lice.  The  last  of  June  a  large  number  of  hills  were  dug 
up  in  this  field,  but  no  root-lice  were  found.  No  injury  was  done  to 
the  seed,  and  a  good  crop  of  corn  was  produced. 

LEROY  EXPERIMENT,  EXAMINATION  OF  JUNE  6,  1907 


Quantities  per  gallon  of  corn 

No.    hills 
examined 

Adult 
ants 

Ant  larvae 

Root-lice 

None   (check)    

50 

638 

0 

7 

l/2   oz.  kerosene    

SO 

294 

400 

0 

54  oz    kerosene  

SO 

641 

500 

14 

3  oz.  10%  solution  oil  of  lemon. 

50 

732 

400 

26 

Experiment  2. — A  40-acre  field,  in  corn  the  preceding  year,  was 
selected  because  of  the  abundance  of  ants'  nests  noticed  in  following 
the  plow,  these  averaging  a  hundred  nests  to  the  mile  of  furrow.  As 
the  plow  used  turned  a  14-inch  furrow,  the  above  number  of  nests  per 
mile  was  approximately  equivalent  to  seven  hundred  per  acre.  The 
field  was  planted  May  9  and  10,  24  rows  with  seed  treated  with  three- 
fourths  of  an  ounce  of  turpentine  to  a  gallon  of  seed;  24  rows  with 
half  an  ounce  of  turpentine  to  the  same ;  16  rows  with  two  ounces  of  a 
10  per  cent  alcoholic  solution  of  oil  of  lemon  to  the  gallon;  20  rows 
with  three  ounces  of  the  same  to  the  gallon;  and  32  rows  with  three 
ounces  of  a  10  per  cent  solution  of  oil  of  citronella  to  the  gallon. 

The  seed  in  this  field  had  begun  to  grow  on  the  17th  of  May,  and 
ants  were  found  at  this  time  in  the  checks  but  not  in  the  treated  plots. 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


423 


On  the  6th  of  June,  on  the  other  hand,  ants  were  found  in  practically 
every  one  of  three  hundred  hills  examined  in  the  various  experimental 
plots,  the  numbers  varying  from  1,657  to  4,163  adults  to  each  lot  of 
fifty  hills,  and  the  ant  larvae  from  850  to  2,500.  Root-lice,  on  the 
other  hand,  varied  from  2  to  241  to  each  lot  of  fifty  hills.  The  totals 
of  these  insects  for  the  three  hundred  hills  are  as  follows :  adult  ants, 
16,935;  ant  larvae,  10,200;  root-lice,  776. 

The  following  table  summarizes  Mr.  Davis's  observations  on  the 
condition  of  the  field  September  17. 

FINAL  TABLE,  EXPERIMENT  No.  2 


CO 

CO 

M 

J^  J3 

<n  n^ 

~  J2 

•jg  IS 

!3g 

rt  ^j 

Treatment 

•**  G 

ig 

«ug 

co 

0  S 
rt 

0  0 

0  0 

.   4-1 

O  ^ 

0  *"" 

0 

nJ  •<-• 

fc  v 

* 

£ 

None    (check)    

200 

149 

140 

9 

Lemon  oil    

100 

130 

131 

2 

Oil  of  citronella  

50 

150 

152 

1 

Turoentine    , 

100 

141 

133 

8 

Experiment  3. — A  field  of  forty  acres,  the  planting  of  which  began 
May  28,  but  was  interrupted  by  rain,  and  recommenced  May  30,  but 
again  interrupted  by  rain.  On  the  6th  of  June,  owing  to  the  wetness 
of  the  weather,  fifteen  acres  of  this  field  still  remained  to  be  planted; 
and  during  the  night  between  the  6th  and  7th  it  rained  again.  This 
remaining  part  of  the  field  was  presently  planted  with  seed  treated 
with  a  10  per  cent  alcoholic  solution  of  oil  of  lemon,  three  ounces  of 
the  mixture  to  the  gallon  of  seed. 

On  the  26th  of  June  ants  were  numerous  in  this  field,  but  no  root- 
lice  were  found.  On  the  3d  of  July  thirty  hills  contained  300  adult 
ants,  175  larvae,  and  125  root-lice.  October  observations  showed  no 
difference  between  the  treated  and  the  untreated  parts  of  the  field, 
either  in  condition  or  in  yield. 

Experiment  4. — Field  planted  on  the  llth  of  May  with  seed 
treated  with  carbolic  acid  at  the  rate  of  three  ounces  per  gallon  of  a 
solution  in  water,  containing  2l/2  to  3  per  cent  of  the  acid. 

On  the  15th  of  June  a  hundred  hills  infested  with  ants  in  this 
field  were  dug  up,  and  root-lice  were  found  in  only  six  of  them.  Later 
counts  of  the  stand  showed  no  difference  between  the  treated  and  the 
untreated  plots,  and  neither  injury  nor  benefit  had  resulted  from  the 
treatment. 


424  BULLETIN  No.  178  [January, 

Experiment  5. — A  farmer's  experiment  in  which  a  field  of  sweet 
corn  was  planted  June  12  and  13  in  alternating  strips  with  untreated 
and  with  treated  seed,  oil  of  lemon  being  used,  a  pint  to  a  gallon  of 
wood  alcohol,  and  about  three  ounces  of  the  mixture  to  the  gallon 
of  corn. 

June  26  the  corn  was  above  the  ground,  and  on  the  5th  of  July 
'  a  hundred  hills  were  dug  up  and  examined,  with  the  result  that  2,205 
adult  ants,  2,070  larvae  and  pupae,  and  763  root-lice  were  found  in  the 
untreated  part  of  the  field,  while  in  the  treated  part  the  adult  ants 
numbered  1,215,  the  larvae  and  pupae  11,  and  the  root-lice  282.  From 
this  it  appears  that  there  was  some  repellent  effect  in  the  seed-corn 
treatment  in  this  field;  but  the  weights  of  corn  from  an  equal  num- 
ber of  hills  from  treated  and  untreated  plots  showed  no  tangible  dif- 
ference in  the  yield,  the  ears  from  four  rows  of  each  weighing 
between  2,100  and  2,200  pounds. 

The  Spring  Weather  at  Leroy. — No  precise  data  of  rainfall  at 
Leroy  were  obtainable  for  May  and  June,  190?,  but  the  notes  of  the 
field  assistants  are  plain  upon  this  point,  as  shown  by  the  following 
extracts : 

May  2  and  3,  work  in  corn  fields  interrupted  by  rain. 

May  14,  rained  hard,  packing  the  ground. 

May  17,  heavy  rain  here  at  night.  Hard  rains  have  apparently 
hejd  the  root-lice  back. 

May  22,  ground  packed  by  hard  rains  and  subsequent  baking. 

May  28,  rain  stopped  planting.  "Big,  heavy  rains  seem  to  have 
killed  the  plant-lice.  Have  noticed  reduction,  in  short,  after  each 
heavy  rain." 

May  30,  cold  and  rains  have  reduced  numbers  of  root-lice. 

May  31,  rain  preceding  night  interrupted  corn  planting. 

June  5,  rain   interrupted   corn   planting. 

June  6,  recent  rains  have  made  fields  too  wet  to  plant. 

June  7,  rained  last  night. 

June  9,  wet  weather  doubtless  the  cause  of  poor  condition  of 
corn. 

June  10,  big  storm. 

June  22,  observations   stopped  by   rain. 

Tune  26,  corn  in  low  ground  apparently  killed  by  water. 

June  27,  field  too  wet  to  cultivate. 

July  9,  corn  on  untilled  field  very  poor  because  of  wet  weather. 

The  fields  under  observation  and  experiment  were  planted  May 
9,  10,  11,  13,  and  14;  May  22,  23,  28,  and  30;  and  June  11,  14,  18, 
and  19. 


/9/5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES  425 

Why  heavy  damage  should  have  been  done  to  seed-corn  at  Nor- 
mal because  of  rains,  while  rainy  weather  did  no  such  harm  at  Leroy 
or  Chenoa,  it  is  impossible  now  to  determine  for  the  lack  of  more 
specific  information  concerning  the  situation  at  those  places. 

LABORATORY  EXPERIMENTS  WITH  THE  EFFECTS  OF  REPELLENTS 

ON  ANTS 

The  substances  used  in  1907  and  1908  in  field  experiments  against 
the  corn-field  ant  had  proved  unsatisfactory,  partly  by  reason  of  the 
uncertainty  of  their  effect  on  the  insects,  but  largely  also  because  of 
the  injury  to  seed-corn  in  wet  weather.  In  the  case  of  the  oil  of 
lemon  an  additional  difficulty  was  an  insufficient  supply  of  the  oil 
and  the  consequent  certainty  that  the  price  would  be  put  up  to  a 
prohibitive  figure  if  there  was  anything  like  a  general  demand  for  it 
at  planting  time.  A  considerable  series  of  experiments  on  ants  was 
consequently  undertaken  in  the  beginning  of  1909  with  a  large 
variety  of  possibly  available  repellents,  with  a  view  to  a  selection  of 
those  most  efficient  and  most  readily  obtainable,  for  further  use  in 
the  field.  As  it  was  desirable  that  the  repellent  effect  should  be  got 
without  the  substance  chosen  actually  touching  the  seed,  the  fluids, 
were  mixed  with  sand  or  other  similar  substance  of  a  kind  to  be 
applied  in  the  field  by  means  of  a  fertilizer-dropper  attached  to  the 
planter  and  dropping  a  powdered  fertilizer  beside  or  over  the  hill. 

All  the  experiments  reported  in  this  section  were  made  by  Mr. 
Maurice  C.  Tanquary,  a  temporary  assistant  of  the  office,  also,  at  the 
time,  a  graduate  student  in  the  University  of  Illinois.  His  work 
began  January  13,  1909,  and  was  carried  on  at  irregular  intervals 
until  the  30th  of  the  following  June.  In  all  of  them,  established 
colonies  of  ants  were  used,  each  consisting  of  worker  ants  and  larvae, 
and  sometimes  containing  also  a  queen.  As  many  previous  experi- 
ments with  the  corn-field  ant  had  shown  that  it  has  a  strong  prefer- 
ence for  orange  light,  in  which,  altho  its  movements  can  be  plainly 
seen  by  us,  it  seems  to  act  as  if  it  were  itself  in  the  dark,  and  as  the 
worker  ants  are  extremely  devoted  to  the  care  of  the  larvae  of  their 
species,  an  apparatus  was  arranged  which  should  take  advantage  of 
these  two  facts  to  afford  a  place  of  comfortable  and  attractive  resort 
such  that  the  repellent  effect  of  the  substances  tested  might  be  shown 
by  driving  the  ants  from  these  comfortable  quarters  into  others  less 
desirable.  It  was  thought  especially  that,  if  they  were  forced  to 
desert  their  larvae,  the  distance  to  which  they  were  driven  by  the 
repellents  and  the  length  of  time  elapsing  before  they  returned  to  the 


426 


BULLETIN  No.  178 


[January, 


care  of  their  helpless  charges,  would  enable  us  to  compare  the  various 
substances  tested  in  respect  to  the  intensity  and  persistence  of  their 
repellent  effects. 

The  apparatus  used  (which  we  may  call  the  cage,  Fig.  1)  was 
essentially  a  shallow,  water-tight  glass  tray,  or  basin,  made  by  build- 
ing a  wall  half  an  inch  high,  with  putty  covered  by  strips  of  glass, 
around  the  edge  of  a  pane  of  glass  16  X  12  inches,  inside  which  another 
pane  of  glass,  8  X  12  inches,  was  supported  at  the  corners  by  pieces 
of  glass  stuck  on  with  balsam.  This  latter  plate  we  will  call  the  base 
of  the  nest  (b).  Its  top  was  a  trifle  below  the  upper  edge  of  the  walls  of 
the  tray,  so  that  water  poured  into  the  latter  until  it  reached  the 
under-surface  of  the  plate  would  surround  it  as  by  a  moat,  which 
prevented  the  escape  of  the  ants  placed  upon  it.  Under  the  center  of 


FIG.  1 

the  transparent  bottom  of  the  cage  was  placed  a  sheet  of  plain  white 
paper  with  concentric  circles  drawn  upon  it,  the  smallest  a  quarter 
of  an  inch  in  diameter,  and  the  succeeding  circles  separated  from 
each  other  by  an  eighth  of  an  inch.  By  the  aid  of  these  circles  one 
could  tell  at  a  glance  the  exact  distance  from  the  center  to  which  any 
ant  had  withdrawn.  Upon  the  center  of  the  base  was  placed  the 
repellent,  and  over  this  a  piece  of  orange  glass,  or  cover,  supported 
at  its  corners  by  bits  of  cork  just  thick  enough  to  allow  the  ants  to 
pass  under  the  cover  conveniently.  The  space  between  the  cover  and 
the  base  is  the  nest  (c).  The  orange  covers  differed  in  size  from  2  X  2^ 
inches  to  2l/z  X  3,  the  latter  being  the  size  used  in  the  following  experi- 
ments unless  other  dimensions  are  given  in  the  descriptions.  In  some 
of  the  cages  used  a  circle  three  inches  in  diameter  was  cut  out  of  the 


t9i  5] 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


419 


The  inference  that  terpeneless  oil  of  lemon,  produced  by  distilling 
off  the  more  volatile  terpenes  from  the  ordinary  oil,  is  more  likely  to 
be  injurious  to  seed-corn  than  either  the  terpenes  or  the  crude  oil,  is 
confirmed  in  an  interesting  manner  by  the  results  of  experiments  de- 
scribed by  Dr.  Whitten  in  the  paper  already  referred  to,  in  which  he 
says:  "At  the  present  the  trend  of  evidence  tends  to  show  that  the 
[corn]  grains  bear  immersion  in  the  lighter  oils  without  injury  for 
much  longer  periods  than  in  the  heavier  oils,  and  that  the  injurious 
after-effects  of  the  latter  are  more  pronounced  than  those  of  the 
former."1 

As  a  general  conclusion  from  this  phase  of  my  discussion,  it  may 
be  said  that  my  supposition  that  injury  to  planted  seed-corn  near 
Bloomington  was  owing  to  differences  in  the  quality  of  the  oils  applied 
to  the  seed,  was  unfounded ;  and  the  cause  of  the  observed  variation  in 
the  effects  of  treatment  must  be  sought  elsewhere. 

As  a  further  test  of  this  conclusion  we  may  take  two  sets  of  plant- 
ings, made  at  the  insectary,  in  which  the  seed  was  treated  with  the 
same  lemon  oils,  in  mixtures  of  the  same  strengths,  as  were  used  by 
Mr.  W.  R.  Scott,  of  Knoxville,  and  Mr.  Frank  Clark,  of  De  Long,  two 
Knox  county  farmers  who  reported  serious  injury  to  their  seed.  Sam- 
ples of  the  oils  were  obtained  from  these  farmers  with  statements  of 
the  strengths  used  by  them.  Both  bought  their  lemon  oil  in  Knox- 
ville, but  from  different  druggists.  From  the  following  table  it  will  be 
seen  that  the  insectary  plantings  of  seed  treated  with  these  oils  yielded 
results  not  materially  different  from  those  of  the  untreated  check- 
plantings  made  at  the  same  time;  and  the  injury  reported  must  hence 
have  been  due  to  some  local  cause. 

POT  PLANTINGS  TREATED  WITH  ORDINARY  LEMON  OIL  AND  ALCOHOL  AS  USED 
BY  W.  R.  SCOTT  AND  FRANK  CLARK.    EXPERIMENT  OF  SEPTEMBER  22,  1907 


*4H     CO 

Per  cent  of  plants  up 

"£  o 

Insectary  test 

.  c 

O  i-* 

'Z  v 

t?  O 

<U    </) 

•* 

September 

October 

r>     V 

1     29 

30 

3 

7 

<.s 

Scott's    sample    

200 

3 

49 

79 

81 

6.2 

Clark's   sample    

600 

2 

21 

76 

79 

5  5 

Checks   

250 

0 

31 

81 

83 

6.1 

'Bulletin,   Illinois   State  Laboratory  of    Natural  History,   Vol.   X,   Art.   V, 
p.  269. 


420  BULLETIN  No.  178  [January, 

CONTRIBUTING   CAUSE  OF   INJURY   TO   SEED-CORN    BY    REPELLENTS 

That  the  cause  was  indeed  local  is  indicated  by  the  fact  that  in  a 
prolonged  trip  through  central  Illinois,  made  during  the  summer  of 
1907,  for  an  inquiry  concerning  the  use  of  lemon  oil  and  its  results, 
Mr.  Davis  found  a  general  complaint  of  injury  to  the  seed  in  the 
vicinity  of  Galesburg,  and  especially  between  Knoxville  and  De  Long. 
In  all  of  the  territory  covered  by  his  trip  the  lemon-oil  treatment  had 
been  more  or  less  used  in  practically  all  localities  except  in  Christian 
county,  and  there  was  commonly  no  report  of  injury  to  the  seed,  the 
main  complaint  of  the  farmers  being  the  fact  that  they  found  no  dif- 
ference in  respect  to  thrift  and  stand  between  treated  and  untreated 
corn. 

What  the  local  cause  of  injury  probably  was  in  these  various  cases 
is  shown  by  the  record  of  rainfall  at  Bloomington,  given  on  a  preced- 
ing page,  taken  in  connection  with  the  proof  contained  in  Dr.  Whit- 
ten's  studies,  already  referred  to,  that  kerosene  and  other  volatile  oils 
are  injurious  to  seed-corn  in  proportion  to  the  amount  of  moisture  in 
the  ground  during  the  planting  and  germinating  period.  In  discussing 
his  own  experiments,  Dr.  Whitten  says : 

"When  the  amount  of  water  in  the  soil  was  reduced  from  30% 
saturation  to  25%  saturation,  the  per  cent,  of  germination  was  increased 
and  the  growth  of  the  seedlings  was  more  nearly  normal;  but  when  the 
water  content  of  the  soil  was  increased  to  50  or  75%  saturation,  the 
per  cent,  of  germination  was  markedly  decreased  and  the  subsequent 
growth  of  many  of  the  seedlings  abnormal."  Again  he  says:  "It  is 
evident  that  within  certain  limits  the  seedlings  are  not  injured  by  the 
oil  present  at  the  time  of  planting,  provided  growth  is  initiated  in  the 
presence  of  a  minimum  amount  of  water.  The  small  quantities  of 
kerosene  are  toxic  in  proportion  to  the  increase  of  the  moisture  con- 
tent of  the  soil.  In  the  50  and  75%  saturated  soils  the  dormant  period 
of  the  grain  is  always  less  than  36  hours,  while  in  the  25%  saturation 
the  time  is  extended  to  approximately  five  days.  This  increase  of  time 
affords  the  seedling  an  opportunity  to  dispose  of  the  oils  much  more 
slowly,  and  it  does  so  without  injurious  effects."1 

The  Bloomington  rainfall  of  nearly  two  and  three-quarters  inches 
distributed  over  seven  days  and  including  the  planting  period  of  the 
Normal  field,  must  have  kept  the  ground  unusually  moist  from  the  be- 
ginning, and  is  a  sufficient  explanation  of  the  injury  to  seed-corn  in 
that  field.  Unfortunately,  I  can  obtain  no  weather  record  of  a  place 


'Bull.  111.  State  Lab.  Nat.  Hist.,  Vol.  X,  Art.  V,  pp.  266-267,  268. 


/p/5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS   INJURIES  421 

where  no  injury  was  done,  for  comparison  with  the  Bloomington  ob- 
servations, and  to  that  extent  the  proof  must  remain  incomplete. 

FIELD    EXPERIMENTS    WITH    REPELLENTS,    1907 

I  have  next  to  report  the  purely  negative  results  of  a  series  of 
field  experiments  and  observations  begun  in  April,  1907,  at  Le  Roy, 
McLean  county,  by  one  of  my  field  assistants,  Mr.  E.  O.  G.  Kelly,  and 
continued  by  Mr.  John  J.  Davis,  to  whom  the  problem  was  transferred 
in  the  latter  part  of  June.  In  these  experiments,  intended  as  a  partial 
repetition  and  verification  of  those  made  at  Elliott,  in  Ford  county,  in 
1906,1  no  injury  was  done  to  the  seed  by  oil  of  lemon  and  alcohol,  oil 
of  citronella  and  alcohol,  carbolic  acid,  pure  kerosene,  or  pure  turpen- 
tine, each  applied  in  the  proportions  commonly  used  by  us  at  this 
time;  nor  was  any  difference  discernible  between  experimental  and 
check  plots  in  the  degree  of  infestation  by  the  ants  or  by  the  aphids. 
Both  the  observers  attributed  the  results  to  heavy  flooding  rains 
which  fell  at  intervals  during  the  whole  planting-period,  and  which 
washed  away  the  fluid  repellents  so  thoroly  that  the  seed  no  longer 
smelled  of  them.  At  the  same  time  root-lice  virtually  disappeared 
from  fields  which  had  been  especially  selected  for  experiment  because 
they  were  so  heavily  infested  by  ants  before  planting  that  it  seemed 
certain  that  the  corn  would  be  seriously  injured  by  root-lice  unless  it 
was  artificially  protected.  Rains  fell  here,  in  short,  at  a  time  and  in  an 
amount  both  to  drown  out  the  root-lice  and  to  wash  away  the  re- 
pellents before  the  seed  could  be  injured. 

The  following  is  an  outline  of  the  more  important  of  these  ex- 
periments. 

Experiment  1. — A  field  of  thirty  acres,  on  which  corn  was  grown 
in  1906,  preceded  by  oats  in  1905.  The  seed  used  in  planting  was 
dealt  with  as  follows :  that  for  16  rows,  was  treated  with  a  fourth 
of  an  ounce  of  kerosene  to  the  gallon  of  seed;  for  24  rows,  with  a 
half  ounce  of  kerosene  to  the  gallon;  for  68  rows,  untreated  and  re- 
served as  a  check;  for  44  rows,  treated  with  three-fourths  of  an  ounce 
of  kerosene ;  for  62  rows,  with  three  ounces  per  gallon  of  a  mixture 
of  oil  of  lemon  (10  per  cent)  and  alcohol  (90  per  cent)  ;  and  for  10 
rows,  untreated,  as  an  additional  check. 

The  field  was  planted  on  the  llth  of  May,  1907,  and  on  the  20th 
of  May  no  odor  of  kerosene  or  oil  of  lemon  could  be  detected  on  the 
treated  seed.  On  the  28th  of  May,  many  hills  were  burrowed  by  ants, 
but  an  examination  of  fifty  such  hills,  dug  up  for  the  purpose,  dis- 


'25th  Rep.  State  Ent.  111.,  p.  14. 


422 


BULLETIN  No.  178 


[January, 


closed  no  root-lice.  On  the  31st  of  May  a  few  root-lice  were  found. 
On  the  6th  of  June  an  examination  of  two  hundred  hills  dug  up  gave 
the  following  averages: 

Check  plots,  50  hills  examined.  Six  hundred  and  thirty-eight 
adult  ants,  no  ant  larvae,  7  root-lice. 

Plot  treated  with  half  an  ounce  of  kerosene  to  the  gallon  of  seed, 
50  hills  examined.  Two  hundred  and  ninety-four  adult  ants,  400 
larvae,  no  root-lice. 

Plot  treated  with  three-fourths  of  an  ounce  of  kerosene  to  the 
gallon  of  seed,  50  hills  examined.  Six  hundred  and  forty-one  adult 
ants,  500  larvae,  14  root-lice. 

Plot  treated  with  a  10  per  cent  solution  of  oil  of  lemon  at  the  rate 
of  three  ounces  per  gallon  of  seed,  50  hills  examined.  Seven  hundred 
and  thirty-two  adult  ants,  400  larvae,  26  root-lice. 

Taking  the  four  plots  together,  2,305  adult  ants  and  1,300  ant 
larvae  were  found  in  two  hundred  hills,  but  these  were  accompanied  by 
only  47  root-lice.  The  last  of  June  a  large  number  of  hills  were  dug 
up  in  this  field,  but  no  root-lice  were  found.  No  injury  was  done  to 
the  seed,  and  a  good  crop  of  corn  was  produced. 

LEROY  EXPERIMENT,  EXAMINATION  OF  JUNE  6,  1907 


Quantities  per  gallon  of  corn 

No.    hills 
examined 

Adult 
ants 

Ant  larvae 

Root-lice 

None   (check)    

SO 

638 

o 

7 

l/2   oz.  kerosene    

50 

294 

400 

0 

54  oz.  kerosene   

SO 

641 

500 

14 

3  oz.  10%  solution  oil  of  lemon. 

50 

732 

400 

26 

Experiment  2. — A  40-acre  field,  in  corn  the  preceding  year,  was 
selected  because  of  the  abundance  of  ants'  nests  noticed  in  following 
the  plow,  these  averaging  a  hundred  nests  to  the  mile  of  furrow.  As 
the  plow  used  turned  a  14-inch  furrow,  the  above  number  of  nests  per 
mile  was  approximately  equivalent  to  seven  hundred  per  acre.  The 
field  was  planted  May  9  and  10,  24  rows  with  seed  treated  with  three- 
fourths  of  an  ounce  of  turpentine  to  a  gallon  of  seed;  24  rows  with 
half  an  ounce  of  turpentine  to  the  same;  16  rows  with  two  ounces  of  a 
10  per  cent  alcoholic  solution  of  oil  of  lemon  to  the  gallon;  20  rows 
with  three  ounces  of  the  same  to  the  gallon;  and  32  rows  with  three 
ounces  of  a  10  per  cent  solution  of  oil  of  citronella  to  the  gallon. 

The  seed  in  this  field  had  begun  to  grow  on  the  17th  of  May,  and 
ants  were  found  at  this  time  in  the  checks  but  not  in  the  treated  plots. 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


423 


On  the  6th  of  June,  on  the  other  hand,  ants  were  found  in  practically 
every  one  of  three  hundred  hills  examined  in  the  various  experimental 
plots,  the  numbers  varying  from  1,657  to  4,163  adults  to  each  lot  of 
fifty  hills,  and  the  ant  larvae  from  850  to  2,500.  Root-lice,  on  the 
other  hand,  varied  from  2  to  241  to  each  lot  of  fifty  hills.  The  totals 
of  these  insects  for  the  three  hundred  hills  are  as  follows :  adult  ants, 
16,935;  ant  larvae,  10,200;  root-lice,  776. 

The  following  table  summarizes  Mr.  Davis's  observations  on  the 
condition  of  the  field  September  17. 

FINAL  TABLE,  EXPERIMENT  No.  2 


«J2 

jn 

(A 

M 

•^  rz3 

C/3    -VH 

•—  *    V—  4 

rs  "^ 

"rt-C 

rt*1* 

^  rs 

Treatment 

45  n 

«8 

«*H   •—  1 

*o  E 

0  o 

0  0 

Jj.^s 

o  ^! 

0  "^ 

O 

132 

£" 

121 

s 

pg 

None    (check)    

200 

149 

140 

9 

Lemon  oil    

100 

130 

131 

2 

Oil  of  citronella  

50 

150 

152 

1 

Turpentine    

100 

141 

133 

8 

Experiment  3. — A  field  of  forty  acres,  the  planting  of  which  began 
May  28,  but  was  interrupted  by  rain,  and  recommenced  May  30,  but 
again  interrupted  by  rain.  On  the  6th  of  June,  owing  to  the  wetness 
of  the  weather,  fifteen  acres  of  this  field  still  remained  to  be  planted; 
and  during  the  night  between  the  6th  and  7th  it  rained  again.  This 
remaining  part  of  the  field  was  presently  planted  with  seed  treated 
with  a  10  per  cent  alcoholic  solution  of  oil  of  lemon,  three  ounces  of 
the  mixture  to  the  gallon  of  seed. 

On  the  26th  of  June  ants  were  numerous  in  this  field,  but  no  root- 
lice  were  found.  On  the  3d  of  July  thirty  hills  contained  300  adult 
ants,  175  larvae,  and  125  root-lice.  October  observations  showed  no 
difference  between  the  treated  and  the  untreated  parts  of  the  field, 
either  in  condition  or  in  yield. 

Experiment  4. — Field  planted  on  the  llth  of  May  with  seed 
treated  with  carbolic  acid  at  the  rate  of  three  ounces  per  gallon  of  a 
solution  in  water,  containing  2l/2  to  3  per  cent  of  the  acid. 

On  the  15th  of  June  a  hundred  hills  infested  with  ants  in  this 
field  were  dug  up,  and  root-lice  were  found  in  only  six  of  them.  Later 
counts  of  the  stand  showed  no  difference  between  the  treated  and  the 
untreated  plots,  and  neither  injury  nor  benefit  had  resulted  from  the 
treatment. 


424  BULLETIN  No.  178  [January, 

Experiment  5. — A  farmer's  experiment  in  which  a  field  of  sweet 
corn  was  planted  June  12  and  13  in  alternating  strips  with  untreated 
and  with  treated  seed,  oil  of  lemon  being  used,  a  pint  to  a  gallon  of 
wood  alcohol,  and  about  three  ounces  of  the  mixture  to  the  gallon 
of  corn. 

June  26  the  corn  was  above  the  ground,  and  on  the  5th  of  July 
a  hundred  hills  were  dug  up  and  examined,  with  the  result  that  2,205 
adult  ants,  2,070  larvae  and  pupae,  and  763  root-lice  were  found  in  the 
untreated  part  of  the  field,  while  in  the  treated  part  the  adult  ants 
numbered  1,215,  the  larvae  and  pupse  11,  and  the  root-lice  282.  From 
this  it  appears  that  there  was  some  repellent  effect  in  the  seed-corn 
treatment  in  this  field;  but  the  weights  of  corn  from  an  equal  num- 
ber of  hills  from  treated  and  untreated  plots  showed  no  tangible  dif- 
ference in  the  yield,  the  ears  from  four  rows  of  each  weighing 
between  2,100  and  2,200  pounds. 

The  Spring  Weather  at  Leroy. — No  precise  data  of  rainfall  at 
Leroy  were  obtainable  for  May  and  June,  1907,  but  the  notes  of  the 
field  assistants  are  plain  upon  this  point,  as  shown  by  the  following 
extracts : 

May  2  and  3,  work  in  corn  fields  interrupted  by  rain. 

May  14,  rained  hard,  packing  the  ground. 

May  17,  heavy  rain  here  at  night.  Hard  rains  have  apparently 
held  the  root-lice  back. 

May  22,  ground  packed  by  hard  rains  and  subsequent  baking. 

May  28,  rain  stopped  planting.  "Big,  heavy  rains  seem  to  have 
killed  the  plant-lice.  Have  noticed  reduction,  in  short,  after  each 
heavy  rain/' 

May  30,  cold  and  rains  have  reduced  numbers  of  root-lice. 

May  31,  rain  preceding  night  interrupted  corn  planting. 

June  5,  rain   interrupted   corn   planting. 

June  6,  recent  rains  have  made  fields  too  wet  to  plant. 

June  7,  rained  last  night. 

June  9,  wet  weather  doubtless  the  cause  of  poor  condition  of 
corn. 

June  10,  big  storm. 

June  22,  observations   stopped  by   rain. 

Tune  26,  corn  in  low  ground  apparently  killed  by  water. 

June  27,  field  too  wet  to  cultivate. 

July  9,  corn  on  untilled  field  very  poor  because  of  wet  weather. 

The  fields  under  observation  and  experiment  were  planted  May 
9,  10,  11,  13,  and  14;  May  22,  23,  28,  and  30;  and  June  11,  14,  18, 
and  19. 


/p/5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES  425 

Why  heavy  damage  should  have  been  done  to  seed-corn  at  Nor- 
mal because  of  rains,  while  rainy  weather  did  no  such  harm  at  Leroy 
or  Chenoa,  it  is  impossible  now  to  determine  for  the  lack  of  more 
specific  information  concerning  the  situation  at  those  places. 

LABORATORY  EXPERIMENTS  WITH  THE  EFFECTS  OF  REPELLENTS 

ON  ANTS 

The  substances  used  in  1907  and  1908  in  field  experiments  against 
the  corn-field  ant  had  proved  unsatisfactory,  partly  by  reason  of  the 
uncertainty  of  their  effect  on  the  insects,  but  largely  also  because  of 
the  injury  to  seed-corn  in  wet  weather.  In  the  case  of  the  oil  of 
lemon  an  additional  difficulty  was  an  insufficient  supply  of  the  oil 
and  the  consequent  certainty  that  the  price  would  be  put  up  to  a 
prohibitive  figure  if  there  was  anything  like  a  general  demand  for  it 
at  planting  time.  A  considerable  series  of  experiments  on  ants  was 
consequently  undertaken  in  the  beginning  of  1909  with  a  large 
variety  of  possibly  available  repellents,  with  a  view  to  a  selection  of 
those  most  efficient  and  most  readily  obtainable,  for  further  use  in 
the  field.  As  it  was  desirable  that  the  repellent  effect  should  be  got 
without  the  substance  chosen  actually  touching  the  seed,  the  fluids 
were  mixed  with  sand  or  other  similar  substance  of  a  kind  to  be 
applied  in  the  field  by  means  of  a  fertilizer-dropper  attached  to  the 
planter  and  dropping  a  powdered  fertilizer  beside  or  over  the  hill. 

All  the  experiments  reported  in  this  section  were  made  by  Mr. 
Maurice  C.  Tanquary,  a  temporary  assistant  of  the  office,  also,  at  the 
time,  a  graduate  student  in  the  University  of  Illinois.  His  work 
began  January  13,  1909,  and  was  carried  on  at  irregular  intervals 
until  the  30th  of  the  following  June.  In  all  of  them,  established 
colonies  of  ants  were  used,  each  consisting  of  worker  ants  and  larvae, 
and  sometimes  containing  also  a  queen.  As  many  previous  experi- 
ments with  the  corn-field  ant  had  shown  that  it  has  a  strong  prefer- 
ence for  orange  light,  in  which,  altho  its  movements  can  be  plainly 
seen  by  us,  it  seems  to  act  as  if  it  were  itself  in  the  dark,  and  as  the 
worker  ants  are  extremely  devoted  to  the  care  of  the  larvae  of  their 
species,  an  apparatus  was  arranged  which  should  take  advantage  of 
these  two  facts  to  afford  a  place  of  comfortable  and  attractive  resort 
such  that  the  repellent  effect  of  the  substances  tested  might  be  shown 
by  driving  the  ants  from  these  comfortable  quarters  into  others  less 
desirable.  It  was  thought  especially  that,  if  they  were  forced  to 
desert  their  larvae,  the  distance  to  which  they  were  driven  by  the 
repellents  and  the  length  of  time  elapsing  before  they  returned  to  the 


426 


BULLETIN  No.  178 


[January, 


care  of  their  helpless  charges,  would  enable  us  to  compare  the  various 
substances  tested  in  respect  to  the  intensity  and  persistence  of  their 
repellent  effects. 

The  apparatus  used  (which  we  may  call  the  cage,  Fig.  1)  was 
essentially  a  shallow,  water-tight  glass  tray,  or  basin,  made  by  build- 
ing a  wall  half  an  inch  high,  with  putty  covered  by  strips  of  glass, 
around  the  edge  of  a  pane  of  glass  16  X  12  inches,  inside  which  another 
pane  of  glass,  8  X  12  inches,  was  supported  at  the  corners  by  pieces 
of  glass  stuck  on  with  balsam.  This  latter  plate  we  will  call  the  base 
of  the  nest  (b).  Its  top  was  a  trifle  below  the  upper  edge  of  the  walls  of 
the  tray,  so  that  water  poured  into  the  latter  until  it  reached  the 
under-surface  of  the  plate  would  surround  it  as  by  a  moat,  which 
prevented  the  escape  of  the  ants  placed  upon  it.  Under  the  center  of 


FIG.  1 

the  transparent  bottom  of  the  cage  was  placed  a  sheet  of  plain  white 
paper  with  concentric  circles  drawn  upon  it,  the  smallest  a  quarter 
of  an  inch  in  diameter,  and  the  succeeding  circles  separated  from 
each  other  by  an  eighth  of  an  inch.  By  the  aid  of  these  circles  one 
could  tell  at  a  glance  the  exact  distance  from  the  center  to  which  any 
ant  had  withdrawn.  Upon  the  center  of  the  base  was  placed  the 
repellent,  and  over  this  a  piece  of  orange  glass,  or  cover,  supported 
at  its  corners  by  bits  of  cork  just  thick  enough  to  allow  the  ants  to 
pass  under  the  cover  conveniently.  The  space  between  the  cover  and 
the  base  is  the  nest  (c}.  The  orange  covers  differed  in  size  from  2  X  2^ 
inches  to  2^/2  X  3,  the  latter  being  the  size  used  in  the  following  experi- 
ments unless  other  dimensions  are  given  in  the  descriptions.  In  some 
of  the  cages  used  a  circle  three  inches  in  diameter  was  cut  out  of  the 


/9/5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES  427 

center  of  the  base,  and  this  was  filled  with  cement  in  a  way  to  make 
a  disk  which,  being  in  contact  with  the  water  beneath,  was  always 
moist.  In  these  cages  the  orange  cover  was  a  circle  of  glass  Zl/2 
inches  in  diameter. 

The  fluid  repellents  were  commonly  applied  by  saturating  fine 
sand  with  them  and  depositing  this  in  a  small  pile  at  the  center  of  the 
nest.  This  was  always  done  after  the  ant  colony  with  its  larvae  in 
charge  had  established  itself  beneath  the  orange  cover. 

The  object  of  these  experiments  being  merely  to  test  the  sub- 
stances in  a  comparative  way,  the  conditions  were  in  all  cases  made 
as  nearly  identical  as  practicable,  especially  with  respect  to  heat  and 
light.  It  is  nevertheless  evident  that  they  are  subject  to  the  disadvan- 
tage that  colonies  of  ants  of  the  same  species  are  not  necessarily  equal 
and  similar  in  their  reactions,  and  that  the  same  colony  may  not  al- 
ways react  in  the  same  way  to  the  same  treatment.  One  of  the  most 
interesting  of  Mr.  Tanquary's  observations  shows  that  the  aspect  of 
the  reaction  may  be  considerably  changed  by  the  exceptional  sensibil- 
ity or  activity  of  only  a  very  few  of  the  individual  ants  of  a  family 
group — only  three  or  four,  perhaps,  out  of  as  many  hundred  rising  to 
the  occasion  and  rescuing  the  young  from  dangerous  or  offensive  situ- 
ations. 

I  have  found  no  way  of  tabulating  or  otherwise  condensing  the 
descriptions  of  Mr.  Tanquary's  notes,  and  can  only  give  the  main  re- 
sults of  the  tests  in  very  general  terms,  referring  the  reader  for  fur- 
ther information  to  the  details  of  the  observations.  Generally  speak- 
ing, then,  it  seems  from  these  experiments  that  oil  of  tansy,  oil  of 
lemon,  anise  oil,  tincture  of  asafetida,  apterite,  and  vermicide  are  very 
strongly  repellent  to  the  corn-field  ant;  that  kerosene,  camphor,  and 
coal-tar  are  strong  repellents,  and  that  the  other  substances  tested  are, 
if  repellent  at  all,  too  slightly  so,  or  for  too  short  a  time,  to  make  them 
promising  materials  for  any  practical  use. 

Experiment  5768^,  Check. — January  13,  1.0:25  a.  m.,  as  a  check 
upon  the  other  experiments,  a  little  sand  moistened  with  water  was  put 
under  an  orange  cover  which  had  been  removed  for  this  purpose  to  a 
fresh  part  of  the  base  at  the  close  of  an  experiment  with  oil  of  lemon. 
The  ants  immediately  began  to  assemble  under  the  cover,  carrying 
their  larvae  with  them ;  but  twenty-seven  of  the  latter  were  thrown  by 
their  nurses  into  the  water,  probably  because  they  still  smelled  of  the 
lemon  oil.  Other  ants  began  at  once  to  carry  out  the  sand  grains  and 


1  The  numbers  here  used  are  those  of  the  "experiment  record"  of  the  office, 
a  book  in  which  all  experiments  are  permanently  recorded. 


428 


BULLETIN  No.  178 


[January, 


scatter  them  about  outside  the  nest.  The  ants  were  not  repelled  by  the 
moist  sand,  but  seemed  to  dislike  its  physical  properties.  By  11:30 
almost  every  particle  of  the  sand  had  been  removed,  and  the  ants  had 
placed  a  few  larvae  on  the  square  of  tin  on  which  the  sand  rested.  By 
1 :  30  p.  m.,  all  the  sand  removed,  some  of  it  being  carried  out  and 
thrown  into  the  water.  One  of  the  three  bunches  of  larvae  under  the 
orange  cover  was  now  on  the  tin.  Time,  3  hours  and  5  minutes. 

Experiment  5762,  Kerosene. — January  13,  1 :  50  p.  m.     A  small 
amount  of  sand  moistened  with  kerosene  was  placed  under  the  center 


FIG.  2 

of  the  orange  cover.  The  ants  nearest  at  once  faced  towards  it,  waved 
their  antennae  about,  and  then  ran  around  in  confusion.  A  very  few  of 
the  ants  approached  the  sand,  and  even  touched  it,  but  quickly  jerked 
back,  throwing  their  antennae  about  vigorously,  seemingly  in  great  dis- 
tress. Others  circled  completely  around  the  sand  at  a  distance  of 
one  or  two  inches.  After  1.5  minutes  a  few  of  the  ants  with  some  of 
their  larvae  were  bunched  under  one  corner  of  the  orange  cover.  In 
55  minutes,  about  a  fourth  of  the  ants  were  under  the  edge  of  the 
cover,  another  fourth  were  an  inch  and  a  half  outside  the  cover,  with 
the  queen,  while  the  other  half  were  assembled  at  a  remote  corner  of 
the  base,  as  shown  in  the  accompanying  sketch  (Fig.  2).  January 
14,  9:45  a.  m.  (19  hours,  5  minutes),  situation  about  as  on  the  previous 
day,  except  that  approximately  half  the  ants  were  under  the  cover, 
none  of  them,  however,  nearer  than  five-eighths  of  an  inch  to  the  re- 
pellent. Most  of  the  ants  under  the  cover  were  in  the  neighborhood 
of  the  queen,  who  was  just  an  inch  from  the  edge  of  the  sand.  The 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS   INJURIES 


429 


average  distance  of  the  ants  from  the  outside  edge  of  the  sand  was 
one  and  an  eighth  inches,  but  the  nearest  ants  were  in  an  approximate 
circle  around  the  sand  at  a  distance  of  five-eighths  of  an  inch.  (Fig  3.) 


JW< 


FIG.  3 

Experiment  5771,  Oil  of  Lemon. — January  12,  4:  15  p.  m.  A  lit- 
tle sand  moistened  with  oil  of  lemon  was  placed  on  the  base,  and  the 
orange  cover  was  moved  to  bring  its  center  over  the  sand.  Within 
three  minutes  nearly  all  the  ants  were  out  from  under  the  cover,  leav- 
ing nearly  all  their  larvae  behind.  A  few  of  the  latter  which  were  so 
far  from  the  sand  that  the  ants  could  get  at  them,  were  brought  to- 
gether near  the  edge  of  the  nest.  Some  of  the  ants  attempted  to  re- 
move the  remaining  larvae,  but  when  they  came  within  an  inch  and  a 
quarter  to  an  inch  and  a  half  of  the  sand  they  stopped,  sometimes 
with  spasmodic  jerkings  of  their  antennae,  and  then  turned  back. 

A  larger  orange  cover,  4X5  inches,  was  placed  over  the  sand  and 
left  over  night.  7:10  a.  m.  (14  hours,  55  minutes),  no  ants  under  the 
cover,  all  being  gathered  along  the  edge  of  the  base.  The  larvae  were 
still  scattered  about  in  the  nest.  8  a.  m.,  orange  cover  replaced  by  an- 
other, 5X6  inches.  9  a.  m.,  the  ants  would  not  go  under  the  cover 
except  that  an  occasional  one  ran  in  for  a  moment  at  the  edge.  A  still 
larger  glass,  6X8  inches,  substituted  for  the  preceding.  11 :  30  a.  m., 
the  ants  were  all  under  one  end  of  the  cover,  as  far  away  as  possible 
from  the  sand,  but  they  had  not  gathered  up  their  scattered  larvae. 
The  position  was  as  shown  by  the  following  sketch  (Fig.  4).  The 
ants  nearest  the  center  of  the  nest  were  constantly  moving  about,  as 
if  dissatisfied,  those  nearer  the  edge  being  quiet.  The  large  cover  was 


430 


BULLETIN  No.  178 


[January, 


now  removed,  together  with  the  repellent,  and  an  orange  cover  2fy  X  3 
inches  was  put  in  its  place.  On  the  following  day,  January  13,  the 
ants  were  all  assembled  in  the  nest. 


Queen' 


s/  6"X  8" 


FIG.  4 

Experiment  5773,  Oil  of  Lemon. — April  26,  1.1 :  12  a.  m.  A  small 
amount  of  sand  moistened  with  oil  of  lemon  placed  under  the  cover, 
within  five-eighths  of  an  inch  of  a  pile  of  larvae.  The  ants  immediately 
began  to  crowd  away,  about  a  sixth  of  the  colony  remaining  under  the 
edge  of  the  cover  an  inch  from  the  sand,  and  the  larvae  being  de- 
serted for  the  time  being.  Four  of  the  workers  soon  began  to  move 
the  larvae  to  the  edge  of  the  nest.  During  32  minutes  but  four  different 
ants  were  seen  carrying  larvae.  After  4  hours  no  ants  remained  under 
the  cover.  They  had  removed  most  of  the  larvae  to  the  edge  of  the 
base,  and  three  of  the  workers  were  engaged  in  carrying  off  the  re- 
mainder. Mr.  Tanquary  remarks  that  very  often  only  a  very  small 
number  of  the  workers — half  a  dozen  or  so — were  active  in  removing 
the  larvae  from  the  neighborhood  of  the  repellent.  In  5  hours  and  18 
minutes  all  the  larvae  had  been  removed.  In  15  minutes  more  some 
ants  were  resting  under  the  corner  of  the  cover.  April  27,  8 :  30  a.  m., 
no  ants  were  under  the  cover.  9:15  (22  hours),  about  twenty  ants 
under  one  corner  of  the  cover.  An  hour  and  5  minutes  later,  about 
two  dozen  ants  were  under  the  cover,  one  and  an  eighth  inches  from 
the  sand.  10 : 25,  the  orange  cover  replaced  with  a  larger  one,  5X6 
inches,  and  food  exposed  at  various  points  under  it  for  the  ants.  11 :  25, 
not  more  than  half  the  ants  are  yet  under  the  cover.  11 :  50,  most  of 
the  ants  are  now  in  the  nest.  3 :  30  p.  m.,  the  large  glass  replaced  by 
one  2l/2  X  3  inches.  4 : 45,  about  half  the  ants  are  under  the  glass. 
April  27,  9:  50  a.  m.,  about  two-thirds  are  under  the  cover  with  the 
larvae,  but  the  others  are  out  on  the  edge  of  the  base.  11:05,  same 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


431 


situation  as  above.     11:24,  about  three-fourths  of  the  ants  are  under 
the  cover.    Repellent  is  removed  and  experiment  closed. 

Experiment  5776,  Oil  of  Lemon. — May  1,  11:  50  a.  m.,  sand  mois- 
tened with  oil  of  lemon  placed  under  the  orange  cover  half  an  inch 
from  the  larvae.  The  ants  scattered  immediately,  most  of  them  leav- 
ing the  nest  entirely,  but  a  few  remained  at  its  corners.  The  larvae 
were  completely  deserted.  Five  minutes  later  a  few  ants  were  under 
each  of  three  corners,  and  three  or  four  were  beginning  to  move  the 
larvae  to  the  corner  of  the  nest.  Most  of  the  ants  were  out  on  the 
corners  of  the  base,  as  shown  in  Figure  5.r  1  hour  and  20  minutes, 


FIG.  5 

fewer  ants  under  the  cover,  most  of  the  larvae  remaining  in  their  origi- 
nal position.  2  hours  and  35  minutes,  situation  unchanged.  In  3  hours 
and  40  minutes  about  a  fourth  of  the  ants  were  under  the  cover,  but 
the  larvae  were  not  yet  gathered  up  (Fig.  6).  Four  hours  and  45 
minutes,  situation  unchanged.  May  3,  9 :  30,  no  ants  under  the  cover, 
but  all  clustered  along  the  edges.  11 : 30  (23  hours  and  40  minutes), 
same  situation.  3:05  p.  m.  (27  hours  and  15  minutes),)  about  two 
dozen  ants  under  one  corner  of  the  cover.  5  p.  m.,  no  ants  under  the 
cover.  May  4,  9  a.  m.,  11 :  55  a.  m.,  3  p.  m.,  and  5 : 15  p.  m.,  situation 
unchanged.  The  ants  have  not  gathered  up  the  larvae  which  they  de- 
serted in  the  beginning.  May  5,  7 : 45,  all  the  ants  gathered  around  the 
edge  of  the  base.  8 :  10,  about  a  dozen  ants  are  under  a  corner  of  the 
cover  nearest  the  larvae.  1 1, :  30,  a  few  of  the  larvae  have  been;  gath- 
ered up  and  transferred  to  a  corner  of  the  nest.  4: 40  p.  m.,  about  two 
dozen  of  the  ants  under  a  corner  of  the  orange  cover  with  about  a 


432 


BULLETIN  No.  178 


[January, 


fourth  of  the  larvae,  which  they  have  gathered  up.  These  larvae  are  an 
inch  and  an  eighth  from  the  sand.  May  6,  9  a.  m.,  nearly  all  of  the 
ants  are  out  on  the  edge  of  the  base.  About  two-thirds  of  the  larvae 
have  been  brought  together  at  a  corner  of  the  nest,  and  about  a  dozen 
ants  are  with  them.  Occasionally  another  larva  is  brought  over  to  the 
corner.  1 1 :  30,  situation  unchanged.  2  p.  m.,  a  few  more  larvae  have 
been  recovered.  5 : 30,  about  a  dozen  ants  in  the  nest  with  larvae,  not 
all  of  which  have  yet  been  recovered.  May  7,  8 :  20  a.  m.,  most  of  the 
larvae  that  had  been  moved  to  the  corner  of  the  nest  are  now  out  on 


Ants  arid  Larvae 


Ants 


FIG.  6 

the  edge  of  the  base,  and  there  are  no  ants  under  the  cover.  1 1 : 30 
a.  m.,  and  5  p.  m.,  situation  unchanged.  May  8,  9  a.  m.,  no  ants  under 
the  cover.  Experiment  closed.  Total  time  nearly  7  days.  [Mr.  Tan- 
quary's  notes  do  not  show  that  the  ants  were  fed  during  this  experi- 
ment.] 

Experiment  5772,  Emulsion  of  Oil  of  Lemon. — April  25,  3 :  50 
p.  m.,  small  amount  of  sand  moistened  with  a  5  per  cent  emulsion  of 
oil  of  lemon  was  placed  under  the  cover.  The  ants  gradually  crowded 
away  from  the  sand.  4  p.  m.,  the  ants  were  three-eighths  of  an  inch 
from  the  sand,  and  were  taking  their  larvae  with  them.  4:10,  the  ants 
were  half  an  inch  from  the  sand.  4:  45,  the  ants  were  withdrawn  an- 
other eighth  of  an  inch.  5 : 45,  same  distance  from  the  sand,  but  not 
so  many  under  the  cover.  April  26,  9:30  a.  m.  (17  hours  and  40 
minutes),  about  half  the  ants  were  under  the  cover,  half  an  inch  from 
the  repellent.  Larvae  three-fourths  of  an  inch  distant.  10:45*  a.  m., 
about  two-thirds  of  the  ants  were  under  the  cover,  the  nearest  a  fourth 


i9i  5\ 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


433 


of  an  inch  from  the  repellent.    The  experiment  was  closed  by  the  re- 
moval of  the  sand,  the  odor  of  which  was  scarcely  distinguishable. 

Experiment  5777 ,  Oil  of  Lemon. — May  27,  2 :  37  p.  m.  This  ex- 
periment was  made  in  a  cage  with  a  3-inch  cement  disk  at  the  center  of 
the  base,  and  a  circular  orange  cover  3^4  inches  across.  Sand  mois- 
tened with  oil  of  lemon  was  placed  beneath  the  center  of  the  cover. 
The  ants  were  thrown  immediately  into  great  confusion,  and  about  half 
of  them  at  first  ran  from  under  the  cover,  deserting  for  a  time  the 
larvae  nearest  the  sand.  These  were  about  one  and  a  fourth  inches  from 
the  repellent.  In  5  minutes  the  ants  on  the  base  were  beginning  to  re- 
turn beneath  the  orange  cover,  some  moving  the  larvae  farther  from 
the  sand  and  recovering  those  at  first  deserted.  After  10  minutes  the 
distance  from  the  sand  to  the  nearest  larva  was  five-eighths  of  an  inch. 
They  were  still  moving  their  larvae  back.  3 : 08,  nearest  larva  now 
six-eighths  of  an  inch.  3  :  40  (63  minutes),  nearest  larva  seven-eighths 
of  an  inch.  Most  of  the  ants  are  out  on  the  base  (Fig.  7,  A).  5  and 


V.i'.Ov  Larvae 


FIG.  7 

5:30,  situation  unchanged.  May  28,  8  a.  m.  (17  hours,  23  minutes), 
larvae  are  more  scattered,  and  the  inner  edge  of  the  pile  is  about  five- 
eighths  of  an  inch  from  the  sand.  About  three- fourths  of  the  ants 
are  under  the  cover  with  them.  2  and  5 :  30  p.  m.,  nearest  larvae  six- 
eighths  of  an  inch  from  the  repellent.  May  29,  8  a.  m.  (41  hours,  23 
minutes),  nearly  all  the  ants  are  under  the  cover.  The  nearest  are 
three-eighths  of  an  inch  from  the  repellent,  as  shown  by  Figure  7,  B. 
1.1 :  50  a.  m.  arid  1 :  30  p.  m.,  situation  unchanged.  5 : 45,  ants  now  all 


434 


BULLETIN  No.  178 


[January, 


under  the  cover,  but  at  the  same  distance  from  the  repellent  as  before. 
May  31,  8  a.  m.,  and  3 :  30  p.  m.,  situation  unchanged.  6  p.  m.  (4  days 
and  3*^5  hours),  ants  same  distance  from  sand,  but  more  dispersed 
(Fig.  7,  C).  June  1,  the  ants  move  about  somewhat  but  maintain  their 
distance  from  the  repellent  all  day  long.  The  same  record  was  made 
for  June  2,  at  8  a.  m.  and  3  p.  m.  (6  days),  when  the  experiment  was 
closed. 

Experiment  5774,  Oil  of  Lemon  and  Bone  Meal. — February  24, 
9:10  a.  m.,  some  bone  meal  soaked  with  oil  of  lemon  was  allowed  to 
dry,  then  moistened  with  water,  and  placed  at  the  center  of  the  nest. 
Most  of  the  ants  escaped  from  under  the  cover,  but  a  third  of  them  re- 
mained under  one  corner  with  the  larvae,  which  were  seven-eighths  of 
an  inch  from  the  bone  meal  (Fig.  8).  In  an  hour  and  fifty  minutes 


FIG.  8 

the  ants  were  about  five-eighths  of  an  inch  from  the  meal,  and  nearly 
half  of  them  were  under  the  cover.  3 :  50  p.  m.,  about  half  the  ants  are 
under  the  cover,  the  nearest  half  an  inch  from  the  fertilizer.  4:  50  (? 
hours,  40  minutes),  situation  unchanged.  February  25,  8  a.  m.,  most 
of  the  ants  are  under  the  cover,  the  nearest  about  half  an  inch  from  the 
fertilizer.  9:30  (24  hours,  10  minutes),  ants  withdrawn  to  about 
three-fourths  of  an  inch.  11  a.  m.,  situation  unchanged  except  that 
fewer  of  the  ants  are  outside  on  the  base.  3:15  and  5  p.  m.,  same  ap- 
pearance. 7:15,  ants  were  about  seven-eighths  of  an  inch  from  the  re- 
pellent, and  about  half  were  now  outside  the  nest.  February  26,  8 
a.  m.,  ants  from  half  an  inch  to  five-eighths  of  an  inch  distant  from  the 
repellent  this  morning.  3 : 30  and  4 :  50  p.  m.  (2  days,  7  hours,  40 


'9/5J 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


435 


minutes),  ants  six-eighths  to  seven-eighths  of  an  inch  distant,  about  a 
third  of  them  outside.  February  27,  8  a.  m.,  about  four-fifths  of  the 
ants  are  under  the  cover  at  a  distance  from  the  repellent  of  three- 
eighths  to  four-eighths  of  an  inch.  4:  50  p.  m.  (3  days  and  nearly  8 
hours),  five-sixths  of  the  ants  now  under  the  cover,  the  nearest  three- 
eighths  to  four-eighths  of  an  inch  from  the  repellent.  Experiment 
closed. 

Experiment  5775,  Oil  of  Lemon  with  Wood  Ashes. — February  24, 
11:10  a.  m.,  wood  ashes  soaked  in  oil  of  lemon,  allowed  to  dry,  and 
moistened  with  water,  placed  at  center  of  nest.  Collection  of  larvae  a 
fourth  of  an  inch  from  the  repellent.  Ants  soon  leave  the  immediate 
vicinity,  deserting  the  larvae.  11 :  30  (20  minutes),  the  nearest  ants  are 
five-eighths  to  six-eighths  of  an  inch  from  the  ashes.  They  have  not 
gathered  up  the  deserted  larvae.  About  two-thirds  of  them  are  under 
the  cover  distributed  as  shown  in  the  accompanying  sketch  (Fig.  9). 


Deserted  La 


FIG.  9 

4:  50  p.  m.  (5  hours,  40  minutes),  ants  are  now  about  seven-eighths  of 
an  inch  from  the  ashes,  but  the  deserted  larvae  have  not  been  recovered 
(Fig.  10).  February  25,  8  a.  m.  (20  hours,  50  minutes),  the  ants  are 
about  three-eighths  of  an  inch  from  the  repellent,  deserted  larvae  not 
recovered.  At  9 :  30  the  ants  are  withdrawn  to  about  three-fourths  of 
an  inch.  At  11  a.  m.,  3:15,  and  5  p.  m.  (29  hours,  50  minutes), 
same  appearance.  7:15  p.  m.  (31  hours  5  minutes),  ants  about  seven- 
eighths  of  an  inch  from  the  repellent,  and  a  larger  number  than  before 
are  outside  the  nest.  February  26,  8  a.  m.,  ants  five-eighths  to  six- 
eighths  of  an  inch  distant  from  the  repellent.  3 :  30  p.  m.,  ants  with- 


436 


BULLETIN  No.  178 


[January, 


drawn  an  inch  and  an  eighth  from  the  repellent,  more  than  half  of 
them  outside  the  nest.  4:  50  p.  m.,  nearest  ants  an  inch  and  an  eighth 
from  the  repellent,  two-thirds  of  them  outside  the  nest.  February  27, 


Deserted  Larvae 


FIG.  10 

8  a.  m.  (2  days,  20  hours,  50  minutes),  most  of  the  ants  are  under  the 
orange  cover,  the  nearest  being  four-eighths  to  five-eighths  of  an  inch 
from  the  repellent.  11 :  50  (3  days,  40  minutes),  ants  distant  from  the 
repellent  three-eighths  to  four-eighths  of  an  inch.  4:  50  p.  m.  (3  days, 
3  hours,  40  minutes),  ants  distant  from  four-  to  five-eighths  of  an  inch. 
Experiment  closed. 

Experiment  5778,  Oil  of  Tansy. — April  17,  8 :  30  a.  m.,  sand 
moistened  with  oil  of  tansy  was  placed  at  the  center  of  a  nest  under 
the  orange  cover  with  a  fresh  colony  of  ants.  Within  four  minutes  all 


FIG.  11 

the  ants  had  left  the  nest,  deserting  a  large  pile  of  larvae  except  for  a 
few  carried  away  as  they  escaped.  8 : 45,  a  number  of  the  ants  go  into 
the  nest  and  walk  about  for  awhile,  but  presently  leave  it,  removing 
none  of  the  larvae.  The  position  of  the  larvae  in  the  nest  is  shown  by 


/p/5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES  437 

the  preceding  sketch  (Fig.  11,  A).  9:15,  a  few  ants  resting  under 
one  corner  of  the  cover  with  a  small  number  of  the  larvae  in  charge 
(Fig.  11,  B).  10:  30  (2  hours),  all  the  ants  but  two  have  left  the  nest, 
deserting  the  larvae.  1.1 :  50,  same  situation.  4  p.  m.  (7  hours,  30 
minutes),  no  ants  under  the  cover.  About  one-third  of  their  larvae 
have  been  carried  out  to  a  corner  of  the  base,  but  the  others  remain  in 
the  nest.  April  22,  2:  45  p.  m.  (5  days,  6  hours,  15  minutes),  the  ants 
have  remained  during  all  this  interval  on  the  corner  of  the  base  with  a 
small  part  of  their  larvae,  and  have  not  gone  near  the  nest.  A  few  of 
them  were  apparently  killed  by  the  tansy  oil.  Repellent  removed,  the 
sand  still  smelling  very  strongly  of  the  oil. 

Experiment  5779,  Oil  of  Tansy. — April  22,  2 :  28  p.  m.,  sand  satu- 
rated with  oil  of  tansy  placed  at  the  center  of  a  nest.  The  ants  scattered 
precipitately,  deserting  the  larvae  and  many  of  them  falling  into  the 
water  around  the  base.  Seventeen  of  the  ants,  some  of  which  in  the 
confusion  rushed  against  the  sand  were  killed  by  the  oil  of  tansy.  The 
others  scattered  over  the  base.  3:10  p.  m.  (42  minutes),  seven  ants 
under  one  corner  of  the  cover.  3  :  45,  4 :  35,  and  5  :  10,  no  ants  under  the 
cover.  April  23,  9  a.  m.  (18  hours,  32  minutes),  no  ants  under  the 
cover.  11:30  a.  m.  (21  hours,  2  minutes),  three  or  four  ants  went 
now  and  then  for  a  little  time  into  one  corner  of  the  nest.  3 : 05  p.  m., 
about  two  dozen  of  the  ants  had  gathered  up  most  of  the  larvae  under 
one  corner  of  the  cover  an  inch  and  an  eighth  from  the  repellent.  All 
the  other  ants  were  out  on  the  base.  April  24,  8  and  11,  a.  m.  (2  days, 
8  hours,  32  minutes),  no  ants  were  in  the  nest.  The  larvae  in  the  cor- 
ner of  the  nest  yesterday  were  piled  on  a  corner  of  the  base.  The 
repellent  was  removed,  the  odor  still  quite  strong.  The  small  cover 
was  replaced  by  an  orange  glass  4X5  inches,  and  food  was  placed  at 
the  center  of  the  nest.  2:  30  p.  m.,  nearly  all  the  ants  had  gathered  in 
the  nest  with  their  larvae. 

Experiment  5789,  Tansy  Tea. — May  24,  tansy  tea  was  prepared 
by  boiling  an  ounce  of  dry  tansy  leaves  for  fifteen  minutes  in  a  quart 
of  water.  The  ants  paid  almost  no  attention  to  sand  moistened  with 
this  infusion,  but  gathered  around  it  as  if  it  were  not  in  the  least  ob- 
jectionable. May  25,  10:  30  a.  m.,  same  situation,  all  the  ants  being  in 
the  nest.  Experiment  closed. 

Experiment  5741,  Tincture  of  Asafetida.—Mzy  4,  1909,  9:25 
a.  m.,  sand  moistened  with  asafetida  was  placed  at  the  center  of  a  nest. 
The  ants  within  began  immediately  to  scatter,  most  of  them  going  out 
on  the  base,  but  some  of  them  rushing  back  and  forth  under  the  orange 
cover.  At  9:45  (20  minutes),  a  few  were  still  running  about  in  the 


438  BULLETIN  No.  178  [January, 

nest,  but  eight  were  lying  on  their  backs  near  the  repellent,  apparently 
overcome  by  the  odor.  At  10: 05  (40  minutes),  practically  all  the  ants 
were  out  on  the  base,  some  of  those  that  were  overcome  struggling 
about,  unable  to  escape.  11  a.  m.,  eleven  ants  were  apparently  dead 
in  the  nest.  At  11:  55,  fourteen  dead  ants  were  seen  under  the  cover. 
By  3:1.5  several  of  those  overcome  had  either  recovered  or  had  been 
carried  out.  At  5:15  (7  hours,  50  minutes),  no  ants  were  in  the  nest. 
The  same  entry  was  made  at  intervals  from  May  5  at  9  a.  m.  to  May  8, 
no  ants  having  entered  the  nest  at  any  time  during  this  interval  of 
four  days  from  the  beginning  of  the  experiment. 

Experiment  5744,  Anise  Oil. — June  30,  1909,  10 :  50  a.  m.  In  this 
experiment  a  large  nest  with  a  cement  bottom  was  used  with  a  cover 
3^4  inches  across.  Sand  moistened  with  anise  oil  was  placed  at  the 
center  of  the  nest.  The  ants  scattered  immediately,  deserting  their 
larvae,  which  were  in  two  piles  two-eighths  and  six-eighths  of  an  inch, 
respectively,  from  the  repellent.  At  11  o'clock  five  ants  were  under 
the  glass  about  the  pile  of  larvae  which  was  farthest  from  the  sand, 
and  others  were  occasionally  running  about  under  the  cover.  At  1 1 :  30 
the  larvae  most  distant  from  the  sand  had  been  moved  out  on  the  base, 
and  no  ants  were  now  under  the  cover.  At  5  p.  m.  (6  hours,  10 
minutes),  all  the  larvae  had  been  removed  from  the  nest  and  no  ants 
were  under  the  cover.  July  7(1  week) ;  up  to  this  time  no  ants  had 
returned  to  the  nest.  This  was  a  weak  colony,  however,  and  the  test 
with  anise  oil  should  have  been  made  again  with  a  larger  number  of 
ants. 

Experiment  5748,  Gum  Camphor. — January  29,  11  a.  m.,  gum 
camphor,  cut  up  into  fine  particles  and  moistened  with  water,  was 
placed  at  the  center  of  a  nest.  The  ants  scattered  immediately,  many 
of  them  running  about  over  the  base  but  most  of  them  hovering  over 
the  larvae  about  three- fourths  of  an  inch  within  the  nest.  At  11 :15  a 
few  ants  were  under  the  corners  of  the  cover  nearest  the  larvae.  At 
11:  50  most  of  the  ants  had  gone  outside  the  nest,  clustering  around 
the  larvae,  but  a  few  were  under  one  corner  of  the  cover,  and  two 
small  companies  were  farther  out  on  the  base.  At  1 :  50  p.  m.  (2  hours, 
50  minutes),  about  one-fourth  to  one-fifth  of  the  ants  were  under  the 
cover,  the  nearest  seven-eighths  of  an  inch  from  the  repellent.  The 
ants  were  in  two  companies,  one  near  the  nest  and  the  other  at  a  cor- 
ner of  the  base  (Fig.  12,  A) ;  and  at  5:30  (6  hours,  30  minutes)  the 
situation  was  unchanged.  On  the  following  day,  January  30,  at  10 :  45 
a.  m.  (23  hours,  45  minutes),  about  half  the  ants  were  gathered  along 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


439 


one  edge  of  the  cover  (Fig.  12,  B)  and  the  others  were  in  two  com- 
panies on  the  base. 


FIG.  12 


Experiment  5753,  Gum  Camphor  in  Solution. — April  20,  at  10 :  35, 
sand  soaked  with  a  saturated  watery  solution  of  gum  camphor  was 


Deserted  Larvae 


Ante  and  Ltrrac 


FIG.  13 


placed  at  the  center  of  a  nest.    The  ants  immediately  left  the  vicinity, 
some  remaining  under  the  edge  of  the  cover  and  the  remainder  escap- 


440  BULLETIN  No.  178  [January, 

ing  from  the  nest.  The  larvae,  which  were  four-eighths  of  an  inch 
from  the  sand,  were  deserted  (Fig.  13,  A).  At  11.  o'clock  about 
one-third  of  the  ants  were  in  the  nest,  as  shown  in  the  figure,  the  near- 
est of  them  five-eighths  of  an  inch  from  the  repellent.  At  11 :  15  a.  m., 
1 :  30  and  2 :  25  p.  m. — 3  hours,  50  minutes — the  nest  presented  practi- 
cally the  same  appearance.  At  3  :  45  (5  hours,  10  minutes),  nearly  all 
of  the  ants  had  left  the  nest  and  a  few  of  the  larvae  had  been  carried 
to  its  outer  edge  (Fig.  13,  B).  At  4:  45  and  at  5:  50 — 7  hours,  15  min- 
utes— about  a  dozen  ants  were  still  in  the  nest.  April  21,  at  9:30 
a.  m.,  no  ants  were  in  the  nest,  the  larvae  having  all  been  carried  out- 
side. At  11 : 30  (24  hours,  55  minutes),  several  ants  had  moved  under 
the  cover  as  shown  in  the  sketch.  At  3 :  30  and  5  p.  m.  the  situation 
was  unchanged.  By  8:  20  a.  m.  April  22  (45  hours,  45  minutes),  about 
three-fourths  of  the  ants  were  in  the  nest,  filling  it  half  way;  at  1.1 
a.  m.  (48  hours,  25  minutes)  the  situation  was  unchanged,  and  the 
experiment  was  closed. 

Experiment  5758,  Formic  Acid. — January  14,  at  10 :  30,  a  small  lot 
of  sand  mixed  with  formic  acid  was  placed  on  the  base,  and  the  orange 
cover  was  moved  over  it  to  form  a  nest  with  the  repellent  at  its  center. 
The  ants  presently  began  to  move  into  the  nest,  but  were  immediately 
affected  by  the  odor  of  the  acid.  Only  two  approached  the  sand  near 
enough  to  touch  it,  and  these  jerked  quickly  back,  vigorously  rubbing 
their  antennae,  which  had  been  brought  in  contact  with  the  acid.  At 
10:45  the  queen  of  the  colony  entered  the  nest  and  the  workers  were 
moving  their  larvae,  all  keeping  as  close  to  the  borders  of  the  nest  as 
practicable,  the  innermost  of  the  assembly  being  always  restless  and 
active.  At  1.1:30  and  at  11:  55  (1  hour,  25  minutes),  the  ants  were 
clustered  at  each  of  the  four  corners  of  the  cover.  At  3:10  p.  m.  (4 
hours,  40  minutes),  nearly  all  the  ants  were  in  the  nest,  a  few  nearer 
the  sand  than  before,  the  nearest  within  two-eighths  to  three-eighths 
of  an  inch.  Some  occasionally  crossed  the  clear  space  within  the  cir- 
cle, and  occasionally  one  even  crawled  over  the  sand,  seemingly  un- 
affected by  its  odor.  By  8:10  the  next  morning  the  ants  were  paying 
no  attention  whatever  to  the  sand,  which  was  removed.  It  had  not 
the  slightest  perceptible  odor,  formic  acid  being  highly  volatile. 

The  experiment  was  repeated  at  8 : 20  a.  m.  of  this  day,  January 
15,  the  ants  immediately  scattering,  about  one-third  of  them  retreat- 
ing to  a  corner  of  the  base.  At  8 :  35  the  ants  were  collected  in  two  of 
the  corners  of  the  nest,  the  queen  among  them,  and  under  the  edge  of 
the  cover  farthest  from  the  repellent,  the  nearest  an  inch  and  an 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


441 


eighth  distant.     The  general  appearance  is  illustrated  by  the  follow- 
ing sketch  (Fig.  14).    At  9:  10  and  10:25  fewer  ants  were  under  the 


'Larvae 


Queen 


FIG.  14 

cover,  and  the  circle  formed  by  them  was  somewhat  larger.  At  1 : 30 
the  distance  between  the  sand  and  the  nearest  ants  was  six-eighths  of 
an  inch,  and  a  few  more  had  entered  the  nest.  At  3  p.  m.  (6  hours,  40 
minutes),  about  half  the  ants  were  under  the  cover,  the  nearest  to  the 


FIG.  15 

repellent  being  three-eighths  to  four-eighths  of  an  inch  away  (Fig. 
15).  Two  ants  were  seen  to  touch  the  sand  with  no  ill  effects.  Ex- 
periment closed. 


442 


BULLETIN  No.  178 


[January, 


Experiment  5750,  Coal-tar. — March  15,  at  '3:50  p  m.,  a  small 
amount  of  coal-tar  was  placed  at  the  center  of  a  nest  under  the  orange 
cover.  The  ants  began  to  leave  the  nest  at  once,  but  only  gradually. 
In  an  hour  and  forty  minutes  all  were  out  of  the  nest  except  about  a 
dozen  which  remained  with  the  larvae,  seven-eighths  of  an  inch  from 
the  tar.  Half  an  hour  later  the  ants  were  carrying  these  larvae  outside. 
By  the  following  morning  at  8:  30  (16  hours,  40  minutes),  about  fifty 
ants  were  in  one  corner  of  the  nest,  distant  five-eighths  of  an  inch 
from  the  repellent,  and  this  condition  remained  unchanged  thru  this 
day.  Twenty-four  hours  later  about  a  fourth  of  the  ants  were  in  the 
nest,  but  during  this  day  they  began  to  withdraw  again,  and  by  8  a.  m. 
of  March  18  all  were  out  of  the  nest  but  two,  which  with  a  few  of 
the  larvae  were  one  and  a  fourth  inches  from  the  tar,  the  other  larvae 
being  outside  on  the  base.  By  1 : 30  of  this  day  these  larvae  had  all 
been  removed,  and  there  was  no  further  change  until  8 : 30  of  the  19th 
(3  days,  16  hours),  when  the  ants  began  to  return,  about  half  of  them 
being  in  the  nest  a  fourth  of  an  inch  or  more  from  the  tar  by  11.:  50  of 
that  day.  Two  days  later,  six  days  from  the  beginning  of  the  experi- 
ment, about  half  the  ants  were  under  the  cover,  together  with  the 
larvae. 

Experiment  5743,  Apterite. — March  5,  at  11:35  a.  m.,  apterite 
moistened  with  water  was  placed  at  the  center  of  a  nest.  The  ants 
were  at  first  not  very  strongly  repelled,  but  soon  began  to  carry  their 


FIG.  16 

larvae  towards  the  edge  of  the  nest.    By  3 :15  all  the  workers  were  out- 
side the  nest  except  four,  which  were  at  one  corner.     Half  of  the 


/p/5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS   INJURIES  443 

others  were  just  outside  on  the  edge  of  the  nest,  and  the  remainder  on 
one  corner  of  the  base.  Most  of  the  larvae  had  been  carried  out,  al- 
tho  a  number  between  an  eighth  and  a  fourth  of  an  inch  from  the 
tar  had  been  left.  (Fig.  16.)  There  was  no  return  of  the  ants  to  this 
nest  up  to  March  11,  6  days  after  the  experiment  was  started.  During 
all  this  period  the  colony  stayed  together  on  a  distant  corner  of  the 
base,  so  closely  packed  that  a  number  were  crowded  off  into  the  sur- 
rounding water  every  day  and  drowned.  When  the  experiment  closed, 
March  11,  only  about  sixty  ants  were  alive. 

Experiment  5790,  Vaporite. — March  5,  at  11:30,  a  bit  of  moist 
vaporite  at  the  center  of  a  nest  disturbed  the  ants  but  did  not  repel 
them  violently.  They  were  mostly  outside  the  nest  together  with  their 
larvse  when  this  was  established,  and  by  3:15  only  half  a  dozen  ants 
had  gone  under  the  cover.  The  rest  remained  outside  until  10 : 45  the 
following  day,  when  about  twenty  were  seen  at  one  corner  of  the  nest 
two  and  a  quarter  inches  from  the  repellent.  By  4:15  of  that  after- 
noon (28  hours,  45  minutes),  there  were  about  fifty  ants  in  the  nest, 
the  nearest  one  and  a  half  inches  from  the  vaporite,  but  all  the  larvae 
were  still  outside  on  the  base.  The  ants  now  gradually  returned,  bring- 
ing their  larvae  with  them,  until  at  9  a.  m.  of  March  7  they  were  all 
in  the  nest.  The  repellent  was  not  removed  until  8 : 45,  March  11,  nearly 
six  days  after  the  experiment  was  begun.  At  this  time  the  ants  nearest 
the  vaporite  were  three-eighths  of  an  inch  away. 

Experiment  5791,  Vermicide. — April  14,  at  8:15  a.  m.,  sand 
soaked  with  vermicide  and  tested  on  a  fresh  colony,  which  had  been  in 
the  cage  for  five  days  only  from  the  field,  drove  them  out  in  less  than 
a  minute,  many  of  their  larvae  being  left  behind  together  with  five  of 
the  workers  which  had  touched  the  vermicide  and  had  then  died.  In 
fifteen  minutes  the  ants  were  beginning  to  carry  their  larvae  out  from 
under  the  cover,  and  piling  them  along  the  border  of  the  nest,  as 
shown  in  the  following  sketch  (Fig.  17).  By  3  p.  m.  there  was 
nothing  in  the  nest  except  some  deserted  larvae  (Fig.  18),  and  these 
conditions  remained  unchanged  until  two  days  had  elapsed,  when  at 
8 :  50  a.  m.  April  16,  a  4  X  4  cover  was  substituted  for  the  smaller  one. 
The  ants  paid  no  attention  to  this  change,  and  the  next  day  at  8 : 20 
a.  m.  a  still  larger  orange  cover  5X6  inches  was  put  in  place.  This 
brought  certain  of  the  ants  under  its  protection  at  one  corner,  and 
others  moved  under  slowly  until  at  9 :  30  about  one-third  of  the  colony 
were  in  the  nest,  the  nearest  two  and  a  fourth  inches  from  the  repel- 
lent. This  condition  remained  practically  unchanged  until  1 1 :  25  April 
19  (5  days,  3  hours),  when  the  small  orange  cover  with  which  the  ex- 


444 


BULLETIN  No.  178 


[January, 


periment  began  was  replaced.     The  sand  seemed  to  have  about  as 
much  odor  as  at  first.    The  ants,  however,  began  to  move  under  slowly, 


*^^&^}S£ 

$$£&£#" 


'  &    Deserted  LA  rvae 

f 


FIG.  17 

and  at  10 :  30  April  20,  some  three-fourths  of  them  were  in  the  nest. 
Experiment  closed. 


•'?•*, 

m 

--     ••'>' 


Deserted  Larvae 


FIG.  18 


Experiment  5752,  Carbon  Bisulfid. — March  26,  this  material,  ap- 
plied as  usual,  drove  the  ants  immediately  out  of  the  nest,  but  owing  to 
its  volatility  it  soon  lost  its  effect,  and  two  hours  and  twenty  minutes 
later  they  were  practically  all  back,  continuing,  however,  to  avoid  the 
immediate  vicinity  of  the  sand  for  several  days. 


79/5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS   INJURIES  445 

Experiments  were  made  with  a  considerable  number  of  additional 
repellents,  to  which  the  ants  reacted  so  feebly  or  for  so  short  a  time 
that  a  detail  of  their  behavior  is  unnecessary.  Among  these  were 
pyrethrum  powder,  calcium  carbide,  capsicum,  iron  sulfate,  chlorid  of 
lime,  and  tobacco,  the  last  applied  in  the  form  of  a  small  piece  of  to- 
bacco plug  which  had  been  soaked  in  water.  In  the  same  class  of  sub- 
stances which  were  more  or  less  disagreeable  to  the  ants,  but  never- 
theless ineffective  as  repellents,  were  the  following  fertilizers:  ground 
limestone,  rock  phosphate,  acid  phosphate,  ground  sheep-manure, 
kainit,  ammonium  sulfate,  dried  blood,  bone  meal,  potassium  sulfate, 
sodium  nitrate,  and  tankage — the  last,  a  vile-smelling  material  from 
the  slaughter-house,  so  little  offensive  to  the  ants  that  many  ©f  them  ap- 
proached and  crawled  over  it  freely,  and  even  placed  their  larvae  in 
contact  with  it.  Later,  they  dealt  with  this  material  as  they  did  in  an- 
other case  with  sand — that  is,  they  carried  it  out  of  the  nest  and  de 
posited  it  on  the  glass  outside  or  threw  it  into  the  water  around  their 
cage.  By  1:15  p.  m.  the  nest  had  been  cleared  and  the  ants  were  all 
at  home. 

ADDITIONAL  FIELD  EXPERIMENTS  WITH  REPELLENTS,  1908 

After  the  failure  of  1907  the  experiments  with  repellents  applied 
to  the  seed  were  repeated  in  1908  on  a  much  larger  scale,  in  the  hope 
of  a  more  favorable  season.  The  spring  proved,  however,  to  be  similar 
to  that  of  the  preceding  year,  and  the  results  were  not  materially  dif- 
ferent. 

In  a  field  of  twenty-five  acres  near  Galesburg,  the  use  of  which 
for  our  purpose  was  secured  by  contract  with  the  owners,  eight  plots 
each  twenty  corn  rows  wide  and  eighty  rods  in  length  were  planted 
on  the  23d  and  25th  of  May  with  seed  treated  with  pure  kerosene, 
kerosene  emulsion,  scalecide,  oil  of  lemon,  carbolic  acid,  and  formalin, 
two  plots  of  twenty  rows  each  being  planted  at  the  same  time  with  un- 
treated seed  as  checks.  These  materials  were  used  in  the  following 
proportions:  kerosene,  1  oz.  to  4  gallons  of  seed;  scalecide,  oil  of 
lemon,  carbolic  acid,  each  in  10  per  cent  alcoholic  solution  of  which  3 
oz.  were  applied  to  a  gallon  of  seed ;  kerosene-soap  emulsion  contain- 
ing 10  per  cent  of  kerosene,  also  3  oz.  to  the  gallon;  and  formalin,  6 
oz.  of  a  3  per  cent  solution  to  the  gallon.  The  original  infestation  of 
this  field,  ascertained  by  Mr.  G.  E.  Sanders,  April  22,  was  at  the  rate 
of  forty-three  nests  to  the  mile  of  furrow. 

The  weather  of  the  spring  at  this  place  preceding  the  date  of 


446  BULLETIN  No.  178  [January, 

planting  is  shown  by  the  following  extract  from  the  field  notes  of  Mr. 
Sanders,  the  responsible  assistant  in  charge  of  this  work. 

April  23,  raining  hard. 

April  24,  rained  steadily  almost  all  day. 

April  27,  raining  more  than  half  the  time  since  11  a.  m.  yester- 
day ;  now  cold  with  some  snow.  Ground  saturated  before  these  rains. 

May  1,  showers  today. 

May  6,  rainy  on  the  4th  and  5th,  the  soil  now  too  wet  for  plowing. 

May  8,  rained  rather  hard  last  night. 

May  14,  rained  very  hard  late  the  preceding  night,  the  ground 
still  too  wet  to  work. 

May  16,  rained  during  the  night. 

May  25,  hard  rain  during  the  night;  too  wet  to  plow  on  the  fol- 
lowing day. 

May  28,  rained  during  the  night  and  all  the  morning.  Also  rained 
on  nights  of  27th,  28th,  and  29th,  and  rained  very  hard  nights  of  June 
6  and  7. 

June  12,  rained  in  the  afternoon. 

June  15,  rains  have  prevented  work  in  the  fields  since  the  10th. 

It  will  be  noticed  that  the  ground  was  planted  on  two  days  after 
an  interval  of  seven  days  since  the  last-mentioned  rain,  but  that  a  hard 
rain  followed  immediately  after  the  planting  was  finished,  and  that 
rain  fell  also  on  the  second,  third,  and  fourth  days  thereafter. 

The  effect  of  the  treatment  of  this  field  was  determined  in  five 
different  ways :  (a)  500  hills  were  examined  in  each  plot  on  each  of 
five  dates  between  June  6  and  July  10,  and  1,000  hills  in  each  plot 
were  examined  June  1.6,  record  being  made  of  the  number  of  hills  out 
of  each  500  found  infested  by  ants ;  (b)  10  hills  infested  by  ants  were 
dug  up  in  each  plot,  including,  of  course,  the  checks,  on  three  dates 
from  June  17  to  July  5,  and  the  number  of  ants  and  root-lice  found  in 
each  of  these  hills  was  determined  by  counting;  (c)  the  stalks  and  the 
vacant  hills  in  500  hills  of  each  plot  were  counted  June  17;  (d)  at 
husking  time,  in  fall,  the  fertile  and  barren  stalks  in  1,000  hills  of  each 
plot,  and  the  ears  borne  by  these  hills,  were  counted,  the  ears  being  dis- 
tinguished as  small,  medium,  and  large;  and  finally  (e)  the  stalks  and 
ears  in  2,000  hills  of  each  plot  were  counted,  and  the  yield  of  ears  for 
each  2,000  hills  was  weighed,  200  hills  being  taken  for  the  purpose 
from  each  of  ten  rows  at  the  center  of  the  20-row  strip. 

As  the  last  test  was  the  most  significant,  its  results  are  first  given 
in  the  following  table. 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


447 


YIELD  OF  TWO  THOUSAND  HILLS  FROM  CENTRAL  Rows  OF  EACH  PLOT 
OF  EXPERIMENTAL  FIELD,  GALESBURG,  1908 


Treatment  of  seed 

Number 
of  stalks 

Number 
of  ears 

Weight  of 
corn  in  pounds 

None    (checks)    

3,695 

2,996 

1,560 

Kerosene    

3,590 

2,767 

1,570 

Carbolic   acid    

3,197 

2,506 

1,450 

Scalecide    

3399 

2690 

1,310 

Kerosene  emulsion    

3,406 

2,478 

1,260 

Oil   of   lemon  

3,422 

2,587 

1,260 

Formalin    

2,039 

1,931 

1,230 

From  this  it  will  be  seen  that  the  check  plots  and  kerosene  plot 
had  the  highest  yields,  and  that  the  other  experimental  plots,  men- 
tioned in  the  order  of  their  yields,  from  highest  to  lowest,  come  as 
follows :  carbolic  acid,  scalecide,  oil  of  lemon,  kerosene  emulsion,  and 
formalin.  Two  thousand  hills  of  the  kerosene  plot  yielded,  indeed, 
ten  pounds  more  than  the  checks,  but  this  difference  is  too  slight  to  be 
taken  into  account.  In  respect  to  the  number  of  stalks  in  each  2,000 
hills,  the  checks  stand  first,  and  the  other  plots  come  in  the  following 
order:  kerosene,  oil  of  lemon,  kerosene  emulsion,  scalecide,  carbolic 
acid,  and  formalin.  The  difference  of  105  stalks  between  the  kerosene 
plot  and  the  checks  is  only  3  per  cent,  and  may  probably  be  disre- 
garded; but  the  difference  of  498  stalks  (13.5  per  cent)  between  the 
checks  and  the  carbolic  acid  plot  is  too  large  to  be  ignored,  while  the 
loss  of  1,656  stalks  in  the  formalin  plot  out  of  a  possible  3,695  (45  per 
cent)  can  only  be  explained  as  due  to  an  original  injury  to  the  seed — 
a  conclusion  confirmed  by  reference  to  an  earlier  examination  of  the 
number  of  stalks  and  missng  hills  in  500  hills  of  each  plot,  made  June 
1.7.  At  this  time,  while  the  checks  averaged  931  stalks  to  this  number 
of  hills,  the  formalin  plot  contained  but  647,  and  while  there  were  41 
missing  hills  in  the  checks  there  were  150  in  the  plot  planted  with 
formalin.  The  loss  in  the  number  of  ears  (36  per  cent)  due  to  the 
formalin  treatment  and  in  the  total  weight  of  the  corn  (21  per  cent) 
puts  this  conclusion  beyond  a  doubt.  The  fact  that  the  loss  in  number 
of  ears  consequent  upon  a  treatment  of  the  seed  with  formalin  was 
less  than  the  loss  in  the  number  of  stalks,  and  that  the  loss  in  weight 
of  the  total  yield  was  still  less  than  that  in  the  number  of  ears,  implies 
that  the  formalin  took  the  greatest  effect  upon  the  poorest  kernels 
which  would  have  produced  the  weakest  plants  and  the  largest  number 
of  barren  stalks. 

Something  of  the  same  tendency  is  shown  in  the  results  of  the 


448  BULLETIN  No.  178  [January, 

carbolic  acid  experiment,  where  the  loss  in  number  of  stalks  was  13 
per  cent  and  that  in  weight  of  the  yield  was  only  7  per  cent.  The 
losses  from  the  other  experiments  of  this  series  were  too  small  for 
such  analysis. 

Our  contract  with  the  owner  of  this  field  provided  that  he  should 
be  reimbursed  for  any  net  loss  of  yield  attributable  to  our  experiments, 
and  a  comparison  of  the  product  of  the  experimental  plots  with  that 
of  the  checks  showing  a  loss  for  the  whole  field  of  60  bushels  and  23 
pounds  of  corn,  a  settlement  was  made  with  him  on  this  basis.  A  tabu- 
lation and  analysis  of  the  data  from  the  earlier  counts  of  hills,  stalks, 
ants'  nests,  ants,  and  aphids  in  the  different  plots  simply  confirm  the 
conclusion  that  no  benefit  was  obtained  from  the  treatment  of  the 
seed-corn  planted  in  this  field  in  1908.  Parallel  experiments  carried 
on  in  this,  field  and  intended  to  test  the  effect  of  deep  cultivation  and 
repeated  harrowing  and  to  show  the  consequences  of  a  rotation  from 
corn  to  oats  will  be  described  later  in  connection  with  other  experiments 
of  the  same  character. 

USE  OF  REPELLENTS  COMBINED  WITH  FERTILIZERS 

The  outcome  of  our  repellent  work  of  1907  and  1908  evidently 
called  for  a  change  of  program.  The  amount  of  the  repellent  sub- 
stances which  could  be  held  by  the  hard,  slightly  absorbent  corn  ker- 
nel was  so  small  that  it  was  easily  washed  away  by  flooding  rains  and 
yet  was  sufficient  to  injure  much  of  the  seed,  if  placed  in  contact  with 
it,  whenever  wet  weather  followed  closely  upon  the  planting.  Either 
the  idea  of  protecting  young  corn  for  a  time  from  ants  and  root-lice 
by  the  use  in  the  hill  of  substances  offensive  to  the  ants  must  be  given 
up,  or  some  safer  repellents  or  safer  and  more  effective  methods  of 
application  must  be  found.  As  there  is  no  possible  advantage  to  the 
seed  itself  to  be  derived  from  the  application  of  repellents  to  it,  the 
corn  kernels  serving  only  as  carriers  of  the  repellent  substances,  it  was 
plain  that  some  other  carrier  might  be  used  to  which  the  repellents 
might  be  applied  more  freely  and  with  less  danger  of  injury  to  the 
seed-corn  or  the  plant;  and  as  it  was  desirable  that  the  use  of  this 
carrier  should  be  worth  while  in  itself,  a  powdered  fertilizer  contain- 
ing ingredients  commonly  needed  on  Illinois  corn  lands  was  selected 
for  the  purpose. 

Experiments  were  begun  along  this  line  in  1910,  by  W.  P.  Flint 
and  G.  E.  Sanders  on  the  farm  near  Galesburg  used  in  the  field  work 
of  1908.  In  traveling  twenty  and  two-thirds  miles  behind  the  plow 
Flint  and  Sanders  counted  in  the  furrow  604  ants'  nests  of  the  corn- 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES  449 

field  ant,  equivalent  to  29.3  nests  to  the  mile  or  207  to  the  acre — a  case 
of  moderate  infestation  only.  The  substances  selected  for  special  trial 
in  this  field  were  those  which  had  been  found  most  offensive  to  ants 
in  the  laboratory  experiments  of  Dr.  Tanquary,  already  described  in 
this  paper.  Choice  was  finally  made  of  tincture  of  asafetida  and  oil 
of  tansy,  applied  to  bone  meal  to  be  dropped  with  the  corn  by  an  at- 
tachment to  the  corn-planter  known  as  a  fertilizer-dropper.  The  bone 
meal  was  used  at  the  rate  of  100  pounds  per  acre,  and  was  treated 
with  the  repellents  as  follows :  Where  oil  of  tansy  was  used,  a  quarter 
of  a  pound  of  the  oil  was  added  to  two  quarts  of  alcohol  and  a  quart 
of  water,  the  fluids  being  then  well  stirred  into  the  hundred  pounds 
of  the  bone  meal  so  as  to  mix  the  whole  mass  thoroly.  The  alcohol 
soon  evaporated,  leaving  the  oil  of  tansy  well  distributed  thru  the 
bone  meal.  The  procedure  with  the  tincture  of  asafetida  was  the  same, 
except  that  the  bone  meal  was  treated  with  two  pints  of  this  fluid 
diluted  with  one  and  a  half  gallons  of  water. 

Plots  containing  3,520  to  5,060  hills  each — -that  is  32  to  46  rows 
wide  and  11.0  hills  long — were  planted  May  12  with  each  of  these  sub- 
stances, and  similar  plots  were  planted  beside  them,  one  with  corn 
accompanied  by  plain  bone  meal  and  the  other  with  no  addition  to  the 
seed. 

At  husking  time  the  yield  of  1,800  hills  taken  from  the  twenty 
central  rows  of  each  plot  was  separately  weighed,  with  the  result  that 
a  considerable  difference  was  shown  in  favor  of  the  plots  which  had 
received  the  repellent  treatment.  The  untreated  plot  yielded  at  the 
rate  of  26.2  bushels;  that  of  the  bone  meal  plot,  26.6  bushels; 
the  bone-meal-asafetida  plot,  31.8  bushels;  and  the  oil  of  tansy  plot, 
37  bushels.  The  gain  was  practically  nothing  for  the  application  of 
plain  bone  meal,  was  5.6  bushels  for  the  use  of  asafetida,  and  10.8 
bushels  for  the  use  of  oil  of  tansy.  The  cost  of  materials  in  these  ex- 
periments was  $1.90  for  the  asafetida  plot,  and  $2.95  for  the  oil  of 
tansy  plot,  the  increase  in  the  yield  of  the  first  being  thus  obtained  at 
34  cents  a  bushel,  and  that  of  the  second  at  27  cents.  The  general  re- 
sult of  this  experimental  change  in  the  method  of  applying  repellents 
at  planting  was  the  more  encouraging  because  the  gains  above  reported 
were  made  during  a  year  quite  unfavorable  to  corn  owing  to  the  very 
poor  stand  obtained.  Cool  weather  after  planting  delayed  germina- 
tion and  gave  moles,  mice,  gophers,  and  insects  an  unusual  opportunity 
to  devour  the  seed  before  it  had  started  to  grow.  However,  as  it  was 
impossible  to  separate  the  loss  due  in  these  unusual  conditions  from 
that  attributable  to  infestation  by  root-lice,  no  exact  estimate  of  re- 


450  BULLETIN  No.  178  [January, 

duced  cost  per  bushel  of  the  increase  can  be  made  for  an  ordinary  year. 

There  was  nothing  in  the  early  inspections  made  to  indicate  any 
loss  or  injury  of  plants  by  these  applications,  and  this  notwithstanding 
the  fact  that  the  weather  of  the  spring  was  on  the  whole  decidedly 
rainy.  The  checks  were  planted  May  11,  and  the  experimental  plots 
on  the  12th.  From  a  complete  meteorological  record  kept  from  April 
16  to  July  2,  by  Mr.  W.  P.  Flint,  who  had  principal  charge  of  these 
experiments  in  the  field,  it  appears  that  the  rainfall  of  the  last  fifteen 
days  of  April  was  an  inch,  and  that  of  May,  4  5/16  inches.  Two  and 
five-sixteenth  inches  of  this  May  rain  fell  during  the  days  of  the 
month  preceding  the  planting  of  the  corn  1^2  inches  on  the  first,  1/16 
of  an  inch  on  the  second,  5/8  of  an  inch  on  the  seventh,  and  1/8  on 
the  tenth.  The  first  rains  to  follow  the  plantings  of  May  11  and  12, 
were  1/8  of  an  inch  on  the  fifteenth  and  3/16  of  an  inch  on  the  six- 
teenth. 

The  complete  record  of  rainfall,  in  inches,  for  the  period  referred 
to  is  as  follows: 

April  16,  snow,  not  measured.  May    16,  3/16  inch. 

17,  9-16  inch.  19,  1/4  inch. 

22,  1-16  inch.  21,  1/16  inch. 

23,  unmeasured  snow.  22,  1/4  inch. 

24,  unmeasured  snow.  23,  trace. 
26,  1/4  inch.  25,  trace. 

30,  1/8  inch.  28,  1. 1/8  inch. 

May      1,  1  1/2  inch.  June     4,  1/8  inch. 

2,  1/16  inch.  8,  1/4  inch. 

7,  5/8  inch.  18,  1/8  inch. 

10,  1/8  inch.  27,  3/4  inch. 

15,  1/8  inch. 

The  temperature  of  ten  days  before  the  planting  period  averaged 
78.6  degrees  F.  as  a  maximum,  41.3  degrees  as  a  minimum,  and  59.95 
degrees  as  the  mean.  Those  for  ten  days  after  the  planting  of  the 
plots  were :  maximum,  83.6 ;  minimum,  48.2 ;  and  mean,  65.9.  The 
maximum  reading  of  the  first  period  was  92  degrees,  and  the  minimum 
was  29.  For  the  second  period  the  maximum  was  97  degrees,  and  the 
minimum,  29.  With  a  rainfall  of  1.7  inches  for  the  first  of  these  ten- 
day  periods  and  a  mean  temperature,  in  the  sun,  of  60  degrees ;  and  a 
rainfall  of  .94  of  an  inch  for  the  second  period  and  a  mean  sunshine 
temperature  of  66  degrees,  the  weather  of  this  planting-time  may 
properly  be  described  as  cool  and  wet.  The  following  is  a  complete 
record  of  temperatures  from  April  16  to  July  2,  as  registered  by  a 


/9/5J  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES  443 

others  were  just  outside  on  the  edge  of  the  nest,  and  the  remainder  on 
one  corner  of  the  base.  Most  of  the  larvae  had  been  carried  out,  al- 
tho  a  number  between  an  eighth  and  a  fourth  of  an  inch  from  the 
tar  had  been  left.  (Fig.  16.)  There  was  no  return  of  the  ants  to  this 
nest  up  to  March  11,  6  days  after  the  experiment  was  started.  During 
all  this  period  the  colony  stayed  together  on  a  distant  corner  of  the 
base,  so  closely  packed  that  a  number  were  crowded  off  into  the  sur- 
rounding water  every  day  and  drowned.  When  the  experiment  closed, 
March  11,  only  about  sixty  ants  were  alive. 

Experiment  5790,  Vaporite. — March  5,  at  11:30,  a  bit  of  moist 
vaporite  at  the  center  of  a  nest  disturbed  the  ants  but  did  not  repel 
them  violently.  They  were  mostly  outside  the  nest  together  with  their 
larvae  when  this  was  established,  and  by  3:15  only  half  a  dozen  ants 
had  gone  under  the  cover.  The  rest  remained  outside  until  10 :  45  the 
following  day,  when  about  twenty  were  seen  at  one  corner  of  the  nest 
two  and  a  quarter  inches  from  the  repellent.  By  4:15  of  that  after- 
noon (28  hours,  45  minutes),  there  were  about  fifty  ants  in  the  nest, 
the  nearest  one  and  a  half  inches  from  the  vaporite,  but  all  the  larvae 
were  still  outside  on  the  base.  The  ants  now  gradually  returned,  bring- 
ing their  larvae  with  them,  until  at  9  a.  m.  of  March  7  they  were  all 
in  the  nest.  The  repellent  was  not  removed  until  8 : 45,  March  11,  nearly 
six  days  after  the  experiment  was  begun.  At  this  time  the  ants  nearest 
the  vaporite  were  three-eighths  of  an  inch  away. 

Experiment  5791,  Vermicide. — April  14,  at  8:15  a.  m.,  sand 
soaked  with  vermicide  and  tested  on  a  fresh  colony,  which  had  been  in 
the  cage  for  five  days  only  from  the  field,  drove  them  out  in  less  than 
a  minute,  many  of  their  larvae  being  left  behind  together  with  five  of 
the  workers  which  had  touched  the  vermicide  and  had  then  died.  In 
fifteen  minutes  the  ants  were  beginning  to  carry  their  larvae  out  from 
under  the  cover,  and  piling  them  along  the  border  of  the  nest,  as 
shown  in  the  following  sketch  (Fig.  17).  By  3  p.  m.  there  was 
nothing  in  the  nest  except  some  deserted  larvae  (Fig.  18),  and  these 
conditions  remained  unchanged  until  two  days  had  elapsed,  when  at 
8 :  50  a.  m.  April  16,  a  4  X  4  cover  was  substituted  for  the  smaller  one. 
The  ants  paid  no  attention  to  this  change,  and  the  next  day  at  8 : 20 
a.  m.  a  still  larger  orange  cover  5X6  inches  was  put  in  place.  This 
brought  certain  of  the  ants  under  its  protection  at  one  corner,  and 
others  moved  under  slowly  until  at  9 :  30  about  one-third  of  the  colony 
were  in  the  nest,  the  nearest  two  and  a  fourth  inches  from  the  repel- 
lent. This  condition  remained  practically  unchanged  until  1 1 :  25  April 
19  (5  days,  3  hours),  when  the  small  orange  cover  with  which  the  ex- 


460  BULLETIN  No.  178  [January, 

size,  planted  at  the  same  time,  having  been  plowed  as  a  check  to  a 
depth  of  four  inches  and  harrowed  once  without  disking.  The  yield 
of  the  latter  was  at  the  rate  of  26.4  bushels  per  acre,  and  of  the  former 
at  the  rate  of  33.15  bushels  per  acre,  a  gain  of  6^4  bushels,  or  nearly 
25  per  cent.  The  cost  of  these  three  diskings  and  one  rolling  was  esti- 
mated at  $1.50  per  acre,  making  the  cost  of  the  increased  yield  22 
cents  a  bushel.  As  there  was  a  poor  stand,  owing  to  the  character 
of  the  spring  weather,  the  cost  of  the  increased  yield  would  have  been 
measurably  less  per  bushel  if  a  fair  stand  and  start  had  been  secured 
in  the  beginning. 

In  another  experiment  made  at  this  same  time  and  place  the  com- 
parative values  of  one,  two,  and  three  diskings  were  brought  into  com- 
parison, the  treatment  of  the  plots  used  being  otherwise  identical.  For 
this  purpose  three  plots,  each  a  hundred  and  sixty  corn-rows  long  by 
thirty-three  rows  wide,  nearly  an  acre  and  a  half  in  area  and  contain- 
ing 5,280  hills,  were  specially  plowed  June  2.  This  ground  had  been 
used  earlier  for  an  experiment  with  fall  plowing  and  disking  as  com- 
pared with  the  same  treatment  in  spring;  and  the  tract  was  now  di- 
vided, to  insure  an  equal  character  and  condition,  into  plots  at  right 
angles  to  the  earlier  ones.  One  of  these,  Plot  9  of  the  year's  series  in 
the  Galesburg  field,  was  plowed  six  inches  deep  June  2,  disked  three 
times,  June  3,  4,  and  6,  with  a  20-inch  disk  to  a  depth  of  five  inches, 
leveled  with  a  toothed  harrow  June  6,  rolled  June  7,  lightly  harrowed 
to  a  depth  of  two  inches  the  same  day,  planted,  and  finally  rolled  after 
planting.  Plot  10  was  treated  in  like  manner  except  that  it  was  disked 
but  twice,  and  Plot  11  differed  only  in  the  fact  that  it  was  disked  but 
once.  Eighty-five  per  cent  of  the  ants'  nests  in  these  plots  were  com- 
pletely turned  out  by  the  six-inch  plowing  and  the  other  15  per  cent 
were  split  by  the  plow,  a  part  of  each  nest  being  left  undisturbed  in 
the  bottom  of  the  furrow.  Fifty  nests  were  marked  in  each  plot  as  it 
was  plowed,  so  that  they  could  be  identified  later  when  the  field  was 
disked. 

At  the  first  disking  45  per  cent  of  these  150  nests,  containing  an 
average  of  21  ants  and  2  larvae  each,  were  found  inhabited,  the  re- 
maining 55  per  cent  of  the  ant  colonies  having  already  disappeared. 
This  observation  indicates  the  effect  of  the  plowing  merely  in  dis- 
persing the  ants  and  breaking  up  their  nests.  Of  the  hundred  marked 
nests  in  plots  9  and  10,  30  per  cent  were  still  inhabited  at  the  second 
disking,  with  an  average  of  12  ants  and  no  larvae  in  each,  70  per  cent 
of  the  colonies  being  now  broken  up  by  the  plowing  and  a  single  disking. 

The  three  plots  of  this  June  planting  encountered  much  better 
weather  than  those  of  the  regular  planting  in  early  May,  and  the  stand 


/9/5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES  461 

was  good  while  that  of  the  May  plantings  was  very  poor.  At  husking 
time  the  yield  of  1,800  hills  taken  from  the  twenty  central  rows  of  each 
plot  was  separately  weighed,  with  the  result  that  the  several  plots 
showed  yields  per  acre  as  follows:  Plot  9  (thrice  disked),  59.75 
bushels;  Plot  1.0  (twice  disked),  60.73  bushels;  Plot  11  (once  disked), 
64.7  bushels.  In  other  words,  the  additional  diskings  beyond  the  first, 
seemed  to  reduce  the  yield  by  6.1  per  cent  for  one  additional  disking, 
and  by  7.7  per  cent  for  two  additional  diskings.  It  would  seem  that 
under  the  circumstances  of  this  experiment,  some  agricultural  disad- 
vantage followed  the  additional  diskings  which  more  than  counter- 
balanced the  advantages  due  to  a  repeated  breaking  up  of  the  nests  of 
the  ants.  Unfortunately  no  fair  check  plot  was  made  for  contrast 
with  the  three  plots  used  in  this  experiment.  It  was  assumed  at  the 
time  that  the  checks  of  the  original  May  planting  would  serve  for  this 
planting  also — a  supposition  disappointed  by  the  great  difference  in 
the  weather  of  the  two  periods. 

EFFECT  OF  FALL  PLOWING  COMPARED  WITH  THAT  OF 
SPRING  PLOWING 

For  the  purpose  of  determining  whether  fall  plowing  and  disk- 
ing of  an  infested  field  was  to  be  preferred  to  spring  treatment,  three 
plots,  Nos.  1,  2,  and  3,  in  this  Galesburg  field,  were  plowed  in  the  fall 
of  1909,  No.  3  to  a  depth  of  four  inches  only,  and  the  others  six 
inches  deep.  Plot  3,  plowed  October  29  and  30,  received  no  further 
treatment  in  the  fall;  but  it  was  necessary  to  disk  it  once  in  spring  in 
order  to  loosen  up  the  plowed  ground,  and  afterwards  to  harrow  it 
before  planting.  Plot  2  was  plowed  October  29,  and  disked  three  times 
in  succession  in  fall,  and  disked  once  in  spring  and  harrowed  also  as 
an  immediate  preparation  for  the  planting  of  the  corn.  Plot  1  was 
disked  three  times  in  fall,  and  rolled  immediately  after  each  disking, 
and  it  was  also  disked  twice  in  spring.  Plot  6,  a  spring-plowed  check 
upon  these  fall-plowed  plots,  was  broken  up  four  inches  deep  May  4, 
and  harrowed  once  before  planting.  All  these  plots  were  planted  on 
the  l.lth  of  May.  Plots  1,  2,  and  3  were  kept  until  the  first  of  June, 
when  the  ground  they  occupied  was  plowed  and  replanted  for  an- 
other experiment,  already  described,  as  plots  9,  10,  and  11. 

In  the  meantime  a  row  of  90  hills  of  corn  was  dug  from  the  cen- 
tral part  of  each  of  these  four  plots  on  each  of  five  different  dates, 
May  23,  25,  28,  30,  and  June  1,  amounting  to  450  hills  for  each  plot; 
and  the  usual  counts  were  made  each  time  of  the  number  of  hills  in- 
fested with  ants,  the  total  number  of  ants  and  aphids  respectively, 


462 


BULLETIN  No.  178 


[January. 


and  the  total  number  of  these  insects  found  in  each  row.     The  follow- 
ing table  gives  the  totals  of  all  these  counts. 

INFESTATION  OF  PLOTS  PLOWED  IN  FALL  AND  IN  SPRING 


No.  of 
plot 

Hills  with 
ants 

Hills  with 
aphids 

Total  No. 
of  ants 

Total  No. 
of  aphids 

1 
2 
3 
6 

SO 
55 
41 
116 

31 
31 
20 
82 

1,125 
1,395 
1,215 
4,150 

348 
310 
295 
1,419 

Fall  plowing 
Fall  plowing 
Fall  plowing 
Spring  plowing 

Plots  3  and  6  differ  only  in  the  fact  that  3  was  fall-plowed  and 
disked  once  in  spring,  while  6  was  spring-plowed  and  not  disked  at  all. 

From  a  comparison  of  the  data  of  these  plots  it  appears  that  the 
fall  plowing  and  single  spring-disking  of  3  had  a  decided  effect  to 
reduce  the  ant  and  root-louse  infestation,  this  being  only  about  a  fourth 
to  a  third  as  great  in  Plot  3  as  it  was  in  6.  On  the  other  hand,  a  com- 
parison of  the  data  for  plots  1,  2,  and  3  shows  practically  no  increased 
advantage  due  to  the  more  thorogoing  treatment  of  plots  1  and  2 
as  compared  with  3. 

ROTATION  OF  CROPS  WITH  FALL  PLOWING 

Advantage  was  taken  by  Mr.  Sanders  at  Galesburg  in  1908  of  the 
fact  that  there  lay  immediately  beside  the  field  used  in  our  experi- 
ments another  field  which  was  to  be  planted  to  corn,  but  which  had 
been  in  oats  in  1907.  For  the  four  years  before  this  it  had  been  in  corn 
continuously,  while  the  experimental  field  had  all  been  in  corn  without 
interruption  since  1904,  and  a  part  of  it  since  1903. 

An  experimental  plot  planted  on  this  oats  stubble,  and  treated  like 
our  checks  and  our  other  experiments,  would  thus  give  us  a  means  of 
judging  of  the  effect  upon  root-aphis  infestation  of  a  change  for  one 
year  from  corn  to  oats.  Such  a  comparison  was  complicated  in  this 
case,  however,  by  the  fact  that  the  oats  field  had  been  all  plowed  in 
the  fall  of  1907,  while  the  experimental  field  was  not  plowed  until  the 
spring  of  1908.  What  was  actually  got  by  planting  a  plot  in  the  oats 
field  was  consequently  a  chance  to  observe  the  apparent  effect  of  rota- 
tion and  fall  plowing  combined. 

This  plot,  like  the  others  beside  it,  was  20  rows  wide  and  200  hills 
long,  thus  containing  4,000  hills.  In  the  fall  of  1907  it  was  merely 
plowed,  to  a  depth  not  stated,  and  on  the  19th  of  the  following  May  it 
was  disked  and  harrowed.  The  two  check  plots  in  the  experimental 


CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES 


463 


field,  each  likewise  containing  2,000  hills,  were  plowed  in  May  to  a 
depth  of  five  inches,  and,  like  the  stubble  plot,  were  disked  once  and 
harrowed.  Another  experimental  plot  of  the  same  size,  known  as  the 
cultivation  plot,  was  plowed  May  12  to  a  depth  of  seven  inches, 
disked  three  times,  on  the  15th,  19th,  and  22d  of  May,  the  disk  work- 
ing the  last  time  to  a  depth  of  four  to  four  and  a  half  inches,  and  har- 
rowed. All  these  plots  were  planted  on  the  22d  and  23d  of  May.  The 
following  table  gives  Mr.  Sanders's  data  of  yield  obtained  November 
15,  when  the  crop  from  these  plots  was  harvested. 

COMPARATIVE  YIELD  OF  CORN  IN  CHECK  PLOTS,  CULTIVA- 
TION  PLOT,  AND  AFTER  OATS,  2,000  HlLLS 

EACH,  GALESBURG,  1908 


Plots 

Stalks 

Ears 

Weight 

Check 

3,712 
3,679 

2,929 
3,064 

1,505 
1,625 

Average 
Cultivation 
Oats 

3,695 
3,794 
3,905 

2,996 
3,074 
3,528 

1,565 
1.720 
1,950 

Compared  with  the  average  yield  of  the  checks,  the  plot  in  the 
fall-plowed  oats  stubble  bore  nearly  6  per  cent  more  stalks  than  the 
checks,  18  per  cent  more  ears,  and  25  per  cent  more  corn  by  weight. 
Compared  with  the  cultivation  plot,  the  differences  in  favor  of  the  stub- 
ble plot  were  nearly  3  per  cent  in  the  number  of  stalks,  more  than  1.1 
per  cent  in  the  number  of  ears,  and  more  than  13  per  cent  in  the 
weight  of  the  crop. 

There  are  several  unknown  elements  capable  of  affecting  this 
comparison,  for  we  know  nothing  of  possible  differences  between  the 
oats  and  corn  fields  in  respect  to  their  fertility  and  other  conditions  due 
to  their  previous  cropping  and  treatment,  and  we  are  also  ignorant  of  the 
possible  influence  of  differences  in  the  weather  at  the  times  when  the 
plowing  was  done  in  fall  and  in  spring.  There  is  additional  evidence, 
however,  that  the  advantage  of  the  stubble  plot  was  due,  at  least  in  part, 
to  the  smaller  number  of  root-lice  harbored  by  it  early  in  the  season. 
Twenty  infested  hills  were  dug  from  each  of  these  plots  and  all  the  ants 
and  aphids  contained  in  them  were  counted  on  the  9th  of  June,  and  again 
on  the  15th  of  that  month,  and  similar  counts  were  made  from  ten  in- 
fested hills  dug  up  in  each  plot  June  23  and  July  5. 


464 


BULLETIN  No.  178 


[January, 


TOTAL  COUNTS  OF  ANTS  AND  APHIDS,  GALESBURG,  JUNE  AND  JULY,  1908 


Plots 

Insects 

June  9(20) 

June  15(20) 

June  23  (10) 

Julys  (10) 

Checks     

Ants 
Aphids 
Ants 
Aphids 
Ants 
Aphids 

583 
564 
588 

153 
15 
159 

861 
819 
1,057 

551 
48 
529 

455 
877 
775 

397 
67 
378 

695 
635 

615 

638 
605 
335 

Oats   

Cultivation  

From  the  above  tabulation  of  the  totals  for  these  dates,  it  will 
be  seen  that  while  the  oats  plot  contained  about  as  many  ants  as  any 
of  the  others,  it  contained  only  about  a  tenth  of  the  number  of  root- 
lice  found  in  the  other  plots  at  the  first  three  counts ;  and  these  were 
no  doubt  migrants  from  the  other  plots  or  the  descendants  of  such 
migrants.  That  it  should  have  been  so  invaded  by  root-lice  from  ad- 
jacent plots  by  the  5th  of  July,  over  forty  days  after  planting,  that 
the  infestation  was  now  virtually  equalized,  is  consistent  with  what 
we  have  found  in  similar  cases,  and  it  illustrates  forcibly  the  fact  that 
no  field  of  corn  is  safe  against  this  insect,  even  tho  it  may  start 
free  from  the  root-lice  in  spring,  as  long  as  adjacent  fields  are  in- 
fested by  it.  Nevertheless,  the  larger  yield  of  the  oat-ground  plot 
than  that  of  the  cultivation  plot  indicates,  as  we  should  anticipate,  that 
rotation  to  oats  makes  in  the  end  a  more  effective  clearance  of  a  field 
than  a  deep  spring  preparation  of  the  soil. 

The  fact  must  not  be  overlooked,  however,  that  rotation  to  small 
grains  acts  slowly  in  spring,  giving  the  ant-aphis  inhabitants  of  the 
field  sufficient  food  for  some  time,  and  ample  opportunity  to  move,  on 
foot  and  on  the  wing,  to  other  fields,  while  deep  and  thoro  stirring 
produces  its  effect  at  once,  before  the  planting-time  of  the  corn,  killing 
and  keeping  down  the  food  plants  of  the  aphids,  and  so  dispersing 
and  disarranging  the  insect  colonies  as  greatly  to  reduce  the  numbers 
of  the  root-lice. 

SUMMARY 

1.  The  principal  measures  of  protection  against  the  corn  root- 
aphis  are  rotation  of  crops ;  an  early  and  deep  plowing,  followed  by 
the  repeated  deep  disking,  of  corn  ground  heavily  infested  by  ants  or 
known  to  have  borne  a  crop  injured  by  the  root-aphis ;  and  the  use  of 
repellent  substances  at  planting-time,  not  by  direct  application  to  the 
seed,  (which  is  dangerous  to  germination  and  early  growth,)  but  by 
previous  mixture  with  chemical  fertilizers  or  other  powdered  sub- 
stances, to  be  dropped  with  the  seed  by  means  of  a  fertilizer-dropper 
attached  to  the  corn-planter.  Pages  405-408. 


I9I5]  CORN  ROOT-APHIS  AND  CONTROL  OF  ITS  INJURIES  465 

2.  Articles  already  published  in  the  Twenty-fourth  and  Twenty- 
fifth  reports  of  the  State  Entomologist's  office  show  marked  benefit  in 
field  experiments  with  deep  plowing  and  repeated  deep  disking,  and 
also  as  a  consequence  of  the  treatment  of  seed-corn  with  oil  of  lemon 
previous  to  planting,  the  last  statement  being  based  upon  a  single  field 
experiment  made  in  1906.  Pages  408-410. 

3.  List  of  operations  described  in  this  paper.    Pages  410  and  411. 

4.  Experiments  of  1907  show  that  wet  weather  at  planting-time 
may  either  result  in  serious  injury  to  the  seed  if  repellents  have  been 
applied  to  it  direct,  or  in  such  washing  away  of  the  repellent  sub- 
stances that  they  produce  no  effect  either  on  the  seed  or  on  the  ants 
and  aphids,  the  character  of  the  effect  apparently  depending  on  the 
amount  of  rainfall  and  on  its  relation  to  the  time  of  actual  planting. 
Comparative   experiments    show    that    the   injurious    effects    reported 
were  not  due,  as  at  first  surmised,  to  differences  in  the  quality  of  the 
repellents  used  in  different  operations.  Pages  411-425. 

5.  Laboratory  experiments  with  a  considerable  variety  of  repel- 
lents applied  by  uniform  methods  to  colonies  of  the  corn-field  ant  in 
a  special  cage,  showed  that  oil  of  tansy,  oil  of  lemon,  anise  oil,  tincture 
of  asafetida,  apterite,  and  vermicide  were  very  strongly  repellent,  that 
kerosene,  camphor,  and  coal-tar  were  less  effective  repellents,  and  that 
a  considerable  number  of  other  substances  tested  were,  if  repellent  at 
all,  too  slightly  so  to  make  them  practically  useful.          Pages  425_44;>. 

6.  Additional  field  experiments  made  in  1908,  in  a  spring  season 
which  proved  to  be  very  wet,  resulted  in  no  injury  to  the  seed,  and  on 
the  other  hand  in  no  benefit  to  the  crop,  flooding  rains  apparently 
washing  away  the  repellents  before  they  could  take  effect  upon  either 
the  seed-corn  or  the  insects.  Pages  445_448 

7.  Experiments  made  in  1910  with  tincture  of  asafetida  and  oil 
of  lemon,  applied  first  to  bone  meal  which  was  then  dropped  with  the 
corn  by  means  of  a  fertilizer-dropper  attachment  to  the  planter,  and 
tested  by  the  yield  at  corn-husking,  showed  a  gain  of  5.6  bushels  per 
acre  by  the  use  of  asafetida,  and  10.8  bushels  per  acre  by  the  use  of 
oil  of  tansy,  the  first  gain  being  obtained  at  a  cost  for  materials  and 
additional  labor  of  thirty-four  cents  a  bushel,  and  the  second  gain  at 
twenty-seven  cents  a  bushel.     This  result  was  the  more  encouraging 
since  a  very  unfavorable  spring  caused  an  unusually  poor  stand  and 
reduced  greatly  the  general  yield  of  corn.     In  a  good  corn  season  the 
gain  would  have  been  greater  for  the  same  cost.  Pages  448-452. 

8.  Additional  experiments  with  deep  plowing  and  repeated  disk- 
ing made  in  1909  showed,  in  one  case,  a  decrease,  due  to  the  treatment, 
of  43  per  cent  in  the  number  of  hills  infested  by  ants,  and  18  per  cent 


466  BULLETIN  No.  178  [January, 

in  the  number  of  ants  in  the  infested  hills,  and  a  decrease  of  27  per 
cent  in  the  number  of  hills  infested  by  root-lice  and  of  9  per  cent  in 
the  number  of  the  root-lice  themselves.  In  another  case  the  number 
of  hills  infested  by  ants  was  reduced  71  per  cent  and  the  number  of 
ants  in  the  infested  hills  83  per  cent,  the  number  of  hills  infested  by 
root-lice  86  per  cent  and  the  number  of  root-lice  in  the  infested  hills 
61  per  cent.  The  same  experiment  showed  that  deep  disking  with  a 
20-inch  disk  was  much  more  effective  in  diminishing  the  number  of 
ants  and  root-lice  than  was  the  comparatively  shallow  disking  of  a 
16-inch  disk,  the  difference  between  the  two  methods  of  treatment 
being  34  per  cent  and  48  per  cent  in  the  number  of  hills  infested  by 
ants  and  by  aphids  respectively,  and  1.3  per  cent  and  35  per  cent  in  the 
number  of  these  insects  themselves.  It  was  incidentally  shown  by 
this  experiment  that  plowing  to  a  depth  of  four  inches  does  not  suf- 
ficiently break  up  the  nests  of  the  ants,  but  that  about  85  per  cent  of 
them  may  be  broken  up  by  plowing  six  inches  deep,  the  remainder 
being  at  least  broken  into.  Pages  452_457. 

9.  Observations  made  at  night  upon  the  movements  of  colonies 
of  ants  out  of  plots  treated  as  above,  and  across  furrows  surrounding 
them,  showed  nearly  two  and  a  half  times  as  many  migrations  from 
the  plots  deeply  stirred  as  from  the  check  plot.    Migration  lines  across 
furrows  plowed  thru  the  center  of  each  of  the  plots  a  week  after 
planting,  showed  the  amount  of  normal  underground  movements  of 
the  ants  at  this  time.     Making  due  allowance  for  this,  it  appears  that 
the  migration  movement  caused  by  the  disturbance   of    the   ants    in 
treated  plots  was  more  than  five  times  as  great  as  this  normal. 

Pages  457-459. 

10.  Plowing  to  a  depth  of  six  inches  in  a  Galesburg  field,  in  1910. 
dispersed  55  per  cent  of  the  ant  colonies  in  this  field,  and  one  disking 
after  plowing  dispersed  15  per  cent  more.     Plowing  six  inches  deep, 
disking  three  times,  and  rolling  once,  increased  the  yield  of  the  plot 
nearly  25  per  cent,  at  a  cost  of  22  cents  a  bushel.     One  20-inch  disk- 
ing followed  by  rolling  gave  all  the  advantages  obtainable  by  addi- 
tional diskings.  Pages  459-461. 

11.  Fall  plowing  and  one  spring  disking  are  much  more  effective 
than  spring  plowing  with  no  disking,  the  latter  containing  about  three 
times  as  many  ants  and  four  times  as  many  aphids  as  the  former. 

Pages  461  and  462 

12.  Change  of  corn  ground  to  oats  for  one  year,  and  fall-plowing 
of  the  oats  stubble,  gave  a  larger  yield  by  25  per  cent  than  adjacent 
ground  kept  continuously  in  corn,  this  difference  being  accompanied 
by  a  root-louse  infestation  of  young  corn  on  the  oats  stubble  about 
one-tenth  that  found  in  corn  on  old  corn  ground.  Pages  462_464. 


UNIVERSITY  OF  ILLINOIS-URBANA 

Q.630.7IL6B  C001 

BULLETIN.  URBANA 
166-181  1914-15 


> 


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•CBS- 

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30112019528436 


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